Washington DC - President Joe Biden claimed Thursday that US and British air strikes against Yemen's Houthis were "defensive" and warned of further measures if they keep attacking ships in the Red Sea.

The Western strikes targeting the Houthis' missile and drone capabilities risked inflaming regional tensions, and came despite Biden's previous warnings against any escalation in the Middle East.

The Houthis say they are responding to Israel's unrelenting assault on Gaza, and have vowed retribution for any attack on their assets in Yemen.

Biden, who is seeking reelection in November, claimed the latest American military intervention in the region was necessary as the Houthi actions would "endanger freedom of navigation in one of the world's most vital waterways."

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"These attacks have endangered US personnel, civilian mariners, and our partners, jeopardized trade, and threatened freedom of navigation," Biden said in a statement.

"I will not hesitate to direct further measures to protect our people and the free flow of international commerce as necessary," the 81-year-old added.

US and British forces struck Yemen again early on Friday, targeting an airbase, airports, and a military camp, the Al-Masirah TV station said.

"Our country was subjected to a massive aggressive attack by American and British ships, submarines and warplanes," said Hussein al-Ezzi, the Houthis' deputy foreign minister.

"America and Britain will have to prepare to pay a heavy price and bear all the dire consequences of this blatant aggression," he added, according to official Houthi media.

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With fighter jets and Tomahawk missiles, 60 targets at 16 Houthi locations were hit by more than 100 precision-guided munitions, US Central Command said in a statement.

Houthi military spokesperson Yahya Saree said at least five people had been killed.

The US strikes have followed an "unprecedented" spate of 27 Houthi attacks on ships in the busy international sea route "including the use of anti-ship ballistic missiles for the first time in history," Biden said on Thursday.

Washington set up an international coalition in December – dubbed Operation Prosperity Guardian – to protect maritime traffic in the area, it said, but the Houthis did not stop.

A joint statement by the US, the UK, Australia, Bahrain, Canada, Denmark, Germany, the Netherlands, New Zealand, and South Korea said the "aim remains to de-escalate tensions."

"But let our message be clear: we will not hesitate to defend lives and protect the free flow of commerce," it said.

Crowds gathered in Times Square in New York City and outside the White House in Washington DC on Thursday to protest the US actions against Yemen.

Chants of "Hands off Yemen" resounded as demonstrators called for an end to American intervention in the Middle East and to US military support for Israel's Gaza campaign.

"Those who bomb those who are trying to stop a genocide are, in fact, part of the genocide, so Joe Biden, when you attack Yemen, it's not a fight against terrorism," ANSWER Coalition National Director Brian Becker said during the DC protest.

"It's a fight to defend the genocidal actions of the reactionary, racist, fascist regime in Tel Aviv," he added.

The rallies happened the same day that South Africa presented its powerful case accusing Israel of genocide before the International Court of Justice in The Hague, Netherlands.

Meanwhile, a federal lawsuit accusing Biden, Secretary of State Antony Blinken, and Defense Secretary Lloyd Austin of complicity in genocide is set to have a hearing on January 26.