by Raul (Pete) Pedrozo | Apr 2, 2025
Oil shipments
Since the Islamic revolution of 1979, the Government of the Islamic Republic of Iran has been hostile to the United States and its allies and partners. It is the leading State sponsor of terror in the world. Iran’s nuclear program additionally poses an existential threat to the United States, as well as to the entire civilized world.
It is therefore in the U.S. national interest to impose maximum pressure on the Iranian regime to end its nuclear threat, curtail its ballistic missile program, and stop its support for terrorist groups. Accordingly, on February 4, 2025, President Trump signed National Security Presidential Memorandum (NSPM)-2. U.S. policy under NSPM-2 is to: 1) deny Iran nuclear weapons and intercontinental ballistic missiles; 2) neutralize Iran’s “network and campaign of regional aggression”; 3) disrupt, degrade, and deny the Islamic Revolutionary Guard Corps and its surrogates “access to the resources that sustain their destabilizing activities”; and 4) “counter Iran’s aggressive development of missiles and other asymmetric and conventional weapons capabilities.”
On February 24, 2025, as part of the maximum pressure campaign, the State Department designated sixteen entities and vessels for their involvement in Iran’s petroleum and petrochemical industry. Concurrently, in coordination with the Department of the Treasury’s Office of Foreign Assets Control, the State Department sanctioned twenty-two persons and identified thirteen vessels as blocked property for their involvement in Iran’s oil industry. Of note, most of the vessels sanctioned are not registered in Iran, but rather fly flags of convenience. These measures, taken pursuant to Executive Orders 13902 and 13846, are intended to disrupt Iran’s ability to collect oil revenues to fund terrorist activities and its nuclear weapons and ballistic missiles programs.
In furtherance of the maximum pressure campaign, the United States announced that it intends to interdict Iranian oil tankers on the high seas to cut off Iran’s oil revenue. The United States will also work with allies and partners to stop Iranian tankers in critical chokepoints like the Straits of Malacca and Singapore. These actions will purportedly be taken under the Proliferation Security Initiative (PSI). By taking these measures, the United States expects to create uncertainty in the market to “deter refiners from purchasing Iranian crude.” While action against foreign-flagged vessels by the United States and other PSI-endorsing States is feasible under PSI, any measures taken against these vessels must be in accordance with national and international law.
Proliferation Security Initiative
President George W. Bush announced the establishment of the PSI on May 31, 2003, as a “global effort that aims to stop trafficking of weapons of mass destruction [WMDs], their delivery systems, and related materials to and from States and non-State actors of proliferation concern.” The initiative was launched, in part, to fill legal gaps in the international counter-proliferation regime exposed during the interdiction of the M/V So San in December 2002. Based on a U.S. request, two Spanish warships stopped the So San in the Arabian Sea. U.S. and Spanish naval personnel boarded the freighter after it was assessed to be a stateless vessel because it was not flying a flag, and its name and nationality were obscured. A subsequent search by the boarding team discovered 15 Scud missiles, 15 warheads, and missile fuel. The vessel and its cargo were released, however, after U.S. and Spanish authorities determined that they lacked clear legal authority to seize the shipment.
The core group of eleven nations, which later grew to twenty-one, developed the Statement of Interdiction Principles (SIP). States become PSI participants by endorsing the SIP, thereby committing “themselves to establish a coordinated and effective basis through which to impede and stop the trafficking in WMDs, their delivery systems, and related material” flowing to and from States and non-State actors of proliferation concern.
Statement of Interdiction Principles (SIP)
PSI participants commit, inter alia, to: 1) take effective measures, either alone or with others, to interdict the transfer or transport of WMD, their delivery systems, and related materials to and from States and non-State actors of proliferation concern; 2) adopt streamlined procedures to rapidly exchange relevant information concerning suspected proliferation activity, dedicate appropriate resources and efforts to interdiction operations and capabilities, and maximize coordination among participants in interdiction efforts; 3) strengthen their relevant national legal authorities to accomplish these objectives, and strengthen relevant international laws and frameworks to support these commitments; and 4) take specific actions, consistent with existing international law and frameworks, in support of interdiction efforts regarding cargoes of WMD, their delivery systems, or related materials, to the extent their national legal authorities permit. For example, States are encouraged to ratify the 2005 Protocol to the Convention for the Suppression of Unlawful Acts Against the Safety of Maritime Navigation (2005 SUA), which criminalizes WMD-related trafficking activities.
Specific actions by a State in support of interdiction efforts include commitments to: 1) exercise flag State authority to prevent the use of its vessels to transport such cargoes; 2) exercise flag State authority to board and search its vessels reasonably suspected of transporting such cargoes and seize such cargoes; 3) provide flag State consent under appropriate circumstances to other States to board and search its vessels and seize such cargoes; 4) exercise coastal State authority to take appropriate actions to stop and/or search foreign-flagged vessels in their internal waters, territorial seas, or contiguous zones, vessels that are reasonably suspected of carrying such cargoes and seize such cargoes; 5) exercise port State authority to enforce conditions on vessels entering or leaving its ports, internal waters, or territorial seas that are reasonably suspected of carrying such cargoes, such as boarding, search, and seizure of such cargoes prior to entry; and 6) exercise port State authority to inspect vessels in port reasonably suspected of carrying such cargoes, and seize such cargoes.
Opposition to PSI
Although PSI has been endorsed by 115 States, it has not achieved universal acceptance and several key States have opposed it. These outliers, while small, are located along strategic sea lanes leading to States of proliferation concern (e.g., Straits of Malacca and Singapore), which diminishes the effectiveness of the PSI interdiction regime. Opposition to the initiative is based on several grounds. Critics argue that SIP is ambiguous in that it lacks details and uses undefined terms and vague language. This leads States to question its “content, meaning, and intention.” Certainly one question that will be raised is whether interdicting oil tankers falls within the remit of PSI and the SIP, which focus on the interdiction of the transfer or transport of WMD, their delivery systems, and related materials to and from States and non-State actors of proliferation concern.
Some States question PSI’s legality, noting that the initiative violates the UN Convention on the Law of the Sea (UNCLOS). These States consider the interdiction provisions of the initiative are inconsistent with high seas freedoms of navigation and the right of innocent passage through the territorial sea. China, for example, is concerned that the PSI interdiction provisions could be used to impede passage of Chinese ships in the territorial seas of PSI-participating States. Because States interpret international law differently, these concerns are not assuaged by the clear language of the SIP that all PSI activities will be taken in accordance with national legal authorities and international law and frameworks. India, moreover, believes that any third-party interdictions in the Indian Ocean would encroach on its primacy in the region.
Other States believe that the initiative lacks legitimacy because it was not established by a UN Security Council resolution. Absent Security Council approval, these States question the legality of conducting nonconsensual interdictions of foreign-flagged vessels at sea. Brazil, for example, prefers a formal non-proliferation mechanism over an informal ad hoc arrangement such as PSI. China has stated that either existing non-proliferation regimes should be improved or a new regime should be established “based on universal participation of all countries and on their decisions made through a democratic process.” Similarly, Indonesia would consider joining PSI but only if the UN was in control.
States like North Korea consider PSI to be a threat to their national security. North Korea directly benefits from the illicit transfer of prohibited items, both financially and militarily. Payments for illicit cargoes provide foreign currency for North Korea’s floundering economy, while WMD-related imports reinforce Pyongyang’s bellicose rhetoric.
Given that PSI-related exercises in the Asia-Pacific region are directed at North Korea, if the initiative is successfully implemented, it would disrupt this “economically and strategically profitable trade.” India has participated in PSI exercises as an observer but has not endorsed the SIP. Despite U.S. assurances to the contrary, Indian officials fear that PSI could be used to target WMD-related cargo to India if there is a shift in U.S. policy. China also considers PSI to impinge on its sovereignty and status as a great power.
Finally, some opponents view PSI as a U.S.-led initiative, which represents unrestrained U.S. power and influence that intrudes on their autonomy and national sovereignty. These States prefer “a more multipolar regional or global order.” Indonesia, for example, opposes PSI because it is a unilateral U.S.-led “regime that falls outside international norms.” Brazil’s “counter-hegemonic” ideology focuses on limiting U.S. influence in “global governance, especially in the Western Hemisphere.” South Africa shares a similar distaste for U.S. influence and power, seeking to assert its own legitimacy in the Global South. PSI’s decision-making process, which is dominated by the United States and its friends and partners is a significant impediment for South Africa’s participation in the initiative. India also views PSI as disproportionately benefitting U.S. power. China’s opposition is similarly based on the view that PSI represents “raw and unconstrained assertion” of U.S. power.
PSI Organizational Structure
PSI is a flexible, voluntary global initiative designed to enhance individual and collective partner States’ capabilities to take appropriate and timely actions to combat WMD proliferation threats. PSI does not create a new international organization with formal membership or a secretariat to run daily operations, nor does it create new law or replace existing nonproliferation regimes (such as the Missile Technology Control Regime, the Nuclear Non-proliferation Treaty, or the 2005 SUA).
Rather, PSI is a multinational response that complements existing counter-proliferation regimes. The initiative is operationally focused and relies on voluntary participation by like-minded States, using existing national and international legal authorities and frameworks to strengthen national capacities to disrupt transfers of WMD, their delivery systems, and related items to and from States and non-State actors of proliferation concern. PSI encourages cooperation between States that are in the best position to act in a given case in their national capacities. PSI additionally conducts exercises and workshops and shares tools and resources to develop States’ capacity to act. Endorsing States are also encouraged to work together to strengthen interdiction-related national and international authorities (e.g., bilateral PSI ship boarding agreements). In short, PSI “provides a platform for networking among States and coordination of their activities to counter proliferation.”
PSI Ship-Boarding Agreements
PSI ship-boarding agreements allow endorsing States to expand their legal authority to interdict illicit shipments at sea. These agreements facilitate securing expedited consent from flag States to inspect their vessels suspected of carrying WMD-related cargoes. The United States has concluded 11 bilateral boarding agreements with key flag States, including the major flags of convenience to allow for boarding and inspecting of suspect ships seaward of the territorial sea of other nations.
Pursuant to these agreements, if a vessel registered in the United States or the partner country is suspected of carrying WMD-related cargo, either party can request the other to confirm the nationality of the ship and authorize the boarding, search, and detention of the vessel and its cargo. As I have noted previously, the boarding provisions vary from agreement-to-agreement from flag State consent being required under all circumstances (i.e., Bahamas and Croatia) to boarding authority being presumed if the flag State does not respond within a certain timeframe (i.e., Belize, Liberia, Marshall Islands, Mongolia, and Panama) to authority to board within a certain period of time if registry cannot be confirmed (i.e., Cyprus, Liberia, Malta, Marshall Islands, Mongolia, and Panama). The only agreement that has been used to support an actual interdiction operation is the agreement with Belize.
Additional Considerations
Clearly, PSI provides a mechanism for the United States to enhance its maximum pressure campaign on Iran by interdicting oil tankers at sea to cut off Tehran’s oil revenues. Although PSI focuses on the transfer or transport of WMD, their delivery systems, and related materials to and from States and non-State actors of proliferation concern, a good argument can be made that oil revenues, which are directly used by Iran to fund its WMD and missile programs, as well as its military support to terrorist organizations like the Houthis, qualify as “related materials” under PSI’s remit.
Regarding shipping activities, many of Iran’s shadow fleet tankers are not registered in Iran but rather fly flags of convenience. If one of these vessels is registered in a PSI-endorsing State with which the United States has a bilateral ship-boarding agreement (e.g., Panama, Marshall Islands, Liberia, Belize), the United States can request permission from the flag State to board, search, and detain the vessel and its cargo consistent with the terms of the agreement.
Similarly, even in the absence of a ship-boarding agreement, a PSI-endorsing State could authorize the United States to exercise jurisdiction over one of its flagged vessels that may be transporting Iranian oil. Generally, a vessel on the high seas is subject to the exclusive jurisdiction of the flag State. Therefore, the flag State, upon request or sua sponte, can grant permission to another State to board and take other enforcement measures against one of its flagged vessels. The United States considers that, as the official representative of the flag State, the master of the vessel has plenary authority over all activities on board the vessel while on the high seas, to include granting consent to board. The scope of master consent, however, is not unlimited. The master can limit the scope, conduct, and duration of the boarding. For example, a master could authorize a boarding and initial inspection of the ship but require flag State consent for any further actions by the boarding State. Therefore, the vessel and its cargo could not be seized without the express consent of the flag State. For non-PSI endorsing States (like Iran, Russia, North Korea, and China) it is unlikely that they would be willing to grant the United States permission to board and take other enforcement measures against their vessels at sea.
If a vessel is stateless, like the So San, it is subject to the jurisdiction of all States. If a warship or other authorized government vessel encounters a foreign vessel beyond the territorial sea of another State, it may board the vessel and take other law enforcement measures if it has reasonable grounds to suspect that the vessel is without nationality. U.S. law expressly provides for jurisdiction over vessels without nationality or a vessel assimilated to be a vessel without nationality. If a shadow fleet tanker 1) does not display a name, flag, or other identifying characteristics; or 2) the master, upon request, fails to make a claim of nationality or registry for the vessel; or 3) the master’s claim of registry or the vessel’s display of registry is denied or cannot be confirmed by the flag State; it can be treated as a vessel without nationality and boarded, inspected, and seized by U.S. authorities.
The United States could also request PSI-endorsing States to take enforcement action against suspect foreign-flagged vessels in their internal waters, territorial sea, archipelagic waters, or contiguous zone, provided that the PSI-endorsing State has domestic laws and regulations authorizing such measures. Coastal States exercise sovereignty over their internal waters and territorial sea. A coastal State may therefore adopt laws and regulations related to innocent passage of foreign-flagged vessels to (inter alia) prevent infringement of its customs and fiscal laws and regulations.
The same rules apply to archipelagic waters. Additionally, in the contiguous zone, coastal States may exercise the control necessary to prevent and punish, inter alia, infringement of its customs and fiscal laws and regulations within its territory or territorial sea. Thus, the United States could request the Philippines, a PSI-endorsing archipelagic State, to take enforcement action against a foreign-flagged vessel operating within its archipelagic waters, provided that Philippine law authorizes such interference.
Similarly, the United States could request PSI-endorsing port States to board and inspect suspect foreign-flagged vessels as a condition on port entry. For ships proceeding to internal waters or a port facility outside internal waters, coastal States may impose conditions on port entry and take the necessary steps to prevent any breach of those conditions. Accordingly, if Singapore has domestic laws or regulations in place that impose conditions on entry on all ships (e.g., all vessels are subject to boarding and inspection upon arrival in port), the United States could request Singapore to take enforcement action against a suspect vessel carrying Iranian oil when it pulls into port.
Conclusion
WMD proliferation constitutes a threat to international peace and security. PSI should therefore not be viewed as a U.S.-led initiative that only serves U.S. interests but rather as a component of the international community’s efforts to curtail the trafficking of WMD-related materials. However, to resonate as an international initiative, the United States must not be seen as acting unilaterally or outside established international legal norms. Any U.S. enforcement action against Iranian tankers, to include boardings and seizures at sea, must be conducted strictly in accordance with U.S. domestic and the international law of the sea, and with the cooperation and support of other PSI-endorsing States.
***
Raul (Pete) Pedrozo is the Howard S. Levie Professor on the Law of Armed Conflict at the Stockton Center for International Law, U.S. Naval War College, Newport, Rhode Island.
The views expressed are those of the author, and do not necessarily reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.
Articles of War is a forum for professionals to share opinions and cultivate ideas. Articles of War does not screen articles to fit a particular editorial agenda, nor endorse or advocate material that is published. Authorship does not indicate affiliation with Articles of War*, the Lieber Institute, or the United States Military Academy West Point.*
Photo credit: U.S. Navy
Print Friendly, PDF & Email