United States 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 Sunday AEDT — 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 comes as the US ramps up sanctions pressure on Tehran while trying to bring it to the negotiating table over its nuclear program.
On his Truth Social platform, Trump warned the group that "your time is up and your attacks must stop", adding "if they don't, hell will rain down upon you like nothing you have ever seen before".
At least 13 civilians were killed and nine injured in US strikes on Yemen's capital Sanaa, according to the 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.
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 the Hamas-Israel war in Gaza.
Iran's other allies, Hamas and Hezbollah in Lebanon, have been severely weakened by Israel since the start of the war. Syria's Bashar al-Assad, who was closely aligned with Tehran, was overthrown by rebels in December.
'The Houthi attack on American vessels will not be tolerated'
Joe Biden's administration had sought to degrade the Houthis' ability to attack vessels off its coast, but limited the US actions.
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 (local time), 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.
