US President Donald Trump has launched strikes against the Houthis in Yemen.
In a post on his Truth Social platform, he also warned Iran the country's support for the group must "end immediately".
The Iran-backed Houthis reported a series of explosions in Yemen's capital Sanaa on Saturday evening.
Images shared online show plumes of black smoke over the area of the city's airport complex, which includes a sprawling military facility.
Mr Trump said the strikes were over the Houthi's attacks against ships in the Red Sea.
"Your time is up, and your attacks must stop, starting today. If they don't, hell will rain down upon you like nothing you have ever seen before," he said.
The president said Iran would be held "fully accountable" for the actions of its proxy, adding: "And we won't be nice about it!"
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The strikes come days after the Houthis said they would resume attacks on Israeli vessels sailing in waters off Yemen in response to Israel's blockade on Gaza, although there have been no Houthi attacks reported since then.
The US, Israel and Britain have previously hit Houthi-held areas in Yemen.
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