Israeli artillery and airstrikes hit south Lebanon on Saturday after Israel said it had intercepted rockets fired from across the border, a clash endangering a shaky truce that ended a year-long war between Israel and Lebanese armed group Hezbollah.
That conflict marked the deadliest spillover of the Gaza war, rumbling across the border for months before escalating into a blistering Israeli offensive that wiped out Hezbollah's top commanders, many of its fighters and much of its arsenal.
Lebanese Prime Minister Nawaf Salam warned of renewed military operations on the southern border, because of the risks they carry "dragging the country into a new war, which will bring woes to Lebanon and the Lebanese people."
"All security and military measures must be taken to show that Lebanon decides on matters of war and peace," he stressed in a statement.
Saturday's exchange was the first since Israel effectively abandoned a separate ceasefire in the Gaza Strip with Palestinian group Hamas, an ally of Hezbollah, both backed by Israel's arch-foe Iran.
The Israeli military said earlier it had intercepted three rockets launched from a Lebanese district about 6 km (4 miles) north of the border, the second cross-border launch since a US-brokered ceasefire in November ended the fighting.
Israel's Army Radio said the military was returning artillery fire. Lebanon's state news agency said Israeli artillery hit two towns in southern Lebanon with airstrikes on three other towns closer to the border.
There were no reports of casualties from either side.
Signaling it could further escalate its response, the Israeli military said it would "respond severely to the morning's attack."
However, the Israeli military said it was still looking into who was responsible for Saturday's cross-border launches towards the northern border town of Metula. Hezbollah did not immediately respond to a Reuters request for comment.
Under the November ceasefire deal, Hezbollah was to have no weapons in southern Lebanon, Israeli troops were to withdraw from the region, and Lebanese army troops were to deploy into the area.
The agreement specifies that Lebanon's government is responsible for dismantling all military infrastructure in southern Lebanon and confiscating all unauthorized arms.
Israeli Defense Minister Israel Katz said the Lebanese government bore responsibility for any rocket salvoes from its territory.
"We will not allow rocket fire from Lebanon on the Galilee communities. We promised security to the communities of the Galilee - and that is exactly how it will be. The rule for Metula is the rule for Beirut," Katz said in a statement.
Israeli army chief Eyal Zamir warned the military would "respond severely" to the attack from Lebanon.
"The IDF (army) will respond severely to the morning's attack," he said in a statement from the military. "The state of Lebanon bears responsibility for upholding the agreement."
The ceasefire brought an end to Israel's intense bombardment and ground operations in Lebanon and Hezbollah's daily rocket barrages into Israel. Each side, however, has accused the other of failing to implement the deal in full.
Israel says Hezbollah still has military infrastructure in the south, while Lebanon and Hezbollah say Israel is occupying Lebanese land by continuing to carry out some airstrikes and keeping its troops at five hilltop positions near the frontier.