President Biden says the US has delivered a "private message" to Iran about the Houthis in Yemen after the US carried out a second strike on the group.
"We delivered it privately and we're confident we're well-prepared," he said without giving further details.
The US said its latest strike was a "follow-on action" targeting radar.
Iran denies involvement in attacks by the Houthis in the Red Sea.
However Tehran is suspected of supplying the Houthis with weapons, and the US says Iranian intelligence is critical to enabling them to target ships.
Joint UK-US airstrikes targeted nearly 30 Houthi positions in the early hours of Friday with the support of Western allies including Australia and Canada.
A day later, the US Central Command said it carried out its latest strike on a Houthi radar site in Yemen using Tomahawk land attack cruise missiles.
UK Foreign Secretary David Cameron said Britain had "no choice" but to take military action against the Houthis in Yemen, in response to their attacks on ships in the Red Sea.
Writing in the Telegraph, he said UK Prime Minister Rishi Sunak had agreed to a request by the US to assist with the "limited and targeted" strikes.
A Houthi spokesman told Reuters the strikes had no significant impact on the group's ability to affect shipping.
The Houthis are an armed group from a sub-sect of Yemen's Shia Muslim minority, the Zaidis. Most Yemenis live in areas under Houthi control. As well as Sanaa and the north of Yemen, the Houthis control the Red Sea coastline.
The official Western government line is that the ongoing air strikes on Houthi targets are quite separate from the war in Gaza. They are "a necessary and proportionate response" to the unprovoked and unacceptable Houthi attacks on commercial shipping in the Red Sea, they say.
In Yemen and the wider Arab world they are viewed rather differently.
There, they are seen as the US and UK joining in the Gaza war on the side of Israel, since the Houthis have declared their actions to be in solidarity with Hamas and the people of Gaza. One theory even says that "the West is doing Netanyahu's bidding".
It is still possible that these airstrikes will have a chilling effect on the Houthis. They will certainly degrade their capacity to attack ships in the short term.
But the longer these airstrikes persist, the greater the risk that the US and UK get sucked into another conflict in Yemen.
It has taken the Saudis more than eight years to extricate themselves from there after it intervened in the country's civil war - and the Houthis are now more entrenched than ever.
About 15% of global seaborne trade passes through the Red Sea, the US says. This includes 8% of global grain, 12% of seaborne oil and 8% of the world's liquified natural gas.
The US says the group has so far attempted to attack and harass vessels in the Red Sea and the gulf of Aden 28 times.
Some major shipping companies have since ceased operations in the region, while insurance costs have risen 10 times since early December.
London and Washington have backed Israel following the 7 October attacks by Hamas in which about 1,300 people were killed and some 240 were taken hostage.
Israel's retaliatory military campaign of air strikes and ground operations against Hamas in Gaza have killed 23,843 Palestinians so far, according to the Hamas-run health ministry on Saturday, with thousands more believed dead under rubble.
Source: BBC
BDST: 1003 HRS, JAN 14, 2024
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