US President Donald Trump has launched large-scale military strikes against Yemen's Iran-aligned Houthis over the group's attacks against Red Sea shipping, killing at least 24 people at the start of a campaign expected to last many days.
Trump also warned Iran, the Houthis' main backer, that it needed to immediately end support for the group.
He said if Iran threatened the US, "America will hold you fully accountable and, we won't be nice about it!"
The strikes on Saturday - which one US official told Reuters might continue for weeks - represent the biggest US military operation in the Middle East since Trump took office in January.
It came as the US ramps up sanctions pressure on Tehran while trying to bring it to the negotiating table over its nuclear program.
"To all Houthi terrorists, 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!" Trump posted on his Truth Social platform.
At least 13 civilians were killed and nine injured in US strikes on Yemen's capital Sanaa, according to the Houthi-run health ministry.
At least 11 others, including four children and one woman, were killed and 14 were injured in a US strike on the northern province of Saada, the Houthi-run Al-Masirah TV reported.
The Houthis' political bureau described the attacks as a "war crime".
"Our Yemeni armed forces are fully prepared to respond to escalation with escalation," it said in a statement.
Residents in Sanaa said the strikes hit a building in a Houthi stronghold.
Another strike on a power station in the town of Dahyan in Saada led to a power cut, Al-Masirah TV reported early on Sunday. Dahyan is where Abdul Malik al-Houthi, the enigmatic leader of the Houthis, often meets his visitors.
The Houthis, an armed movement that took control of most of Yemen over the past decade, have launched scores of attacks on ships off its coast since November 2023, disrupting global commerce and setting the US military on a costly campaign to intercept missiles and drones that have burned through stocks of US air defences.
A Pentagon spokesperson said the Houthis have attacked US warships 174 times and commercial vessels 145 times since 2023.
The Houthis say the attacks are in solidarity with Palestinians over Israel's war in Gaza with Hamas militants.
Iran's other allies, Hamas and Hezbollah in Lebanon, have been severely weakened by Israel since the start of the Gaza conflict. Syria's Bashar al-Assad, who was closely aligned with Tehran, was overthrown by rebels in December.
Yemen's Houthis have sunk two vessels, seized another and killed at least four seafarers in an offensive that disrupted global shipping, forcing firms to reroute to longer and more expensive journeys around southern Africa.
Joe Biden's administration had sought to degrade the Houthis' ability to attack vessels off its coast but limited the US actions.
US officials, speaking on condition of anonymity, say Trump has authorised a more aggressive approach.
The strikes were carried out in part by fighter aircraft from the Harry S Truman aircraft carrier, with the US military's Central Command describing the strikes as the start of a large-scale operation across Yemen.
"Houthi attacks on American ships & aircraft (and our troops!) will not be tolerated; and Iran, their benefactor, is on notice," Defense Secretary Pete Hegseth wrote on X. "Freedom of Navigation will be restored."
Trump held out the prospect of far more devastating military action against Yemen.
"The Houthi attack on American vessels will not be tolerated. We will use overwhelming lethal force until we have achieved our objective," Trump wrote.
Iran's Foreign Minister Abbas Araqchi said the US government had "no authority, or business, dictating Iranian foreign policy".
On Tuesday, the Houthis said they would resume attacks on Israeli ships passing through the Red Sea and Arabian Sea, the Bab al-Mandab Strait and the Gulf of Aden, ending a period of relative calm starting in January with the Gaza ceasefire.
The US attacks came just days after a letter to Iran's Supreme Leader Ayatollah Ali Khamenei from Trump was delivered, seeking talks over Iran's nuclear program.
Khamenei on Wednesday rejected holding negotiations with the US.
