Donald Trump has said the US would hold Iran directly responsible for any future attacks carried out by the Houthi group that it backs in Yemen, and that Tehran would "suffer the consequences".
Responding to the Houthi movement's threats to international shipping, the US launched a new wave of air strikes on Saturday, killing at least 53 people.
Describing the Houthis as "sinister mobsters and thugs", Mr Trump wrote on his Truth Social website that any attack by the group would be met with "great force, and there is no guarantee that that force will stop there".
"Iran has played 'the innocent victim' of rogue terrorists from which they've lost control, but they haven't lost control," Mr Trump said in his post.
"They're dictating every move, giving them the weapons, supplying them with money and highly sophisticated military equipment, and even, so-called, 'Intelligence.'"
In a letter seen by Reuters, Iran has reportedly told the United Nations Security Council that Mr Trump and other US officials had made "reckless and provocative statements" that levelled "baseless accusations" and threatened the use of force against Tehran.
"Iran strongly and categorically rejects any accusation on the violation of relevant Security Council resolutions on arms embargoes in Yemen or involvement in any destabilising activities in the region," Iran's UN ambassador Amir Saeid Iravani wrote.
The White House said that Mr Trump's message to Iran was to take the United States seriously.
The Pentagon said it had struck over 30 sites so far and would use overwhelming lethal force against the Houthis until the group stopped attacks.
The Pentagon's chief spokesperson, Sean Parnell, said the goal was not regime change.
The Houthis also launched drones and missiles targeting the USS Harry S Truman aircraft carrier in the Red Sea, though none reached the ship.
The head of Iran's paramilitary Revolutionary Guard sought to separate the Houthis' actions from those of Tehran this weekend.
Houthi supporters themselves rallied in several cities after the strikes, vowing revenge against America and Israel over blocking aid to the Gaza Strip.
The Houthis' al-Masirah satellite news channel put young boys on air live, who chanted the group's slogan: "God is the greatest; death to America; death to Israel; curse the Jews; victory to Islam."
"The Yemeni position is an irreversible position [regarding Gaza], so do whatever you [Americans] want, for we are men who fear no one but God," said Mohammed Ali al-Houthi, a Houthi leader who spoke to the demonstration in Yemen's rebel-held capital, Sanaa.
The Houthi rebels attacked over 100 merchant vessels with missiles and drones, sinking two vessels and killing four sailors, from November 2023 until January this year when a ceasefire began in Gaza.
The campaign also greatly raised the Houthis' profile in the wider Arab world and tamped down on public criticism against their human rights abuses and crackdowns on dissent and aid workers.
The Houthis claimed there had been additional US air strikes overnight, though American officials did not immediately acknowledge them.
