American navy helicopters sank three small boats used by Houthi militants to attack a Maersk container vessel in the southern Red Sea, the US military has said.
Several of the armed Houthi crews were killed when the helicopters opened fire, the US military added.
There have been no injuries on the Denmark-owned container vessel.
The ship was targeted as Iranian-backed Houthi militants in Yemen have stepped up attacks on vessels in the Red Sea to show their support for the Palestinian militant group Hamas, which is fighting Israel in Gaza.
The Maersk Hangzhou ship initially reported it had been hit by a missile on Saturday evening in the southern Red Sea, around 55 nautical miles from Yemen, US Central Command (Centcom) said in a statement.
The USS Gravely and USS Laboon responded to a distress call and the Maersk vessel was found to be seaworthy, the statement added.
The US military also said it shot down two anti-ship missiles that were fired towards the container ship.
Hours later the Maersk vessel issued a second distress call when it was targeted by four Houthi boats.
The Houthi militants fired small arms weapons at the Maersk Hangzhou, getting to within about 65ft (20m) of the vessel, Centcom said.
A contract-embarked security team on the ship returned fire, the central command said.
Helicopters from the USS Eisenhower aircraft carrier and the USS Gravely responded to the distress call and, while issuing verbal warnings to the attackers, the small boat crews opened fire on the helicopters using small arms, the statement said.
“The US navy helicopters returned fire in self-defence”, sinking three of the four boats, killing the crews, while the fourth boat fled the area, Centcom said, and no damage to US personnel or equipment was reported.
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Maersk has paused all sailing through the Red Sea for 48 hours after the latest attack.
The Singapore-flagged vessel with capacity to carry 14,000 containers was travelling from Singapore to Port Suez.
UK Foreign Secretary David Cameron said he had spoken to his Iranian counterpart about attacks in the Red Sea “which threaten innocent lives and the global economy”.
He added: “I made clear that Iran shares responsibility for preventing these attacks given their long-standing support to the Houthis.”
The Iranian-backed Houthis say their attacks are aimed at Israel-linked ships in an effort to stop the Israeli offensive in Gaza.