An RAF Typhoon aircraft takes off from RAF Akrotiri airbase in Cyprus, for a mission to strike targets in Yemen. AP

The United States and Britain launched strikes from the air and sea against Houthi military targets in Yemen in response to the movement's attacks on ships in the Red Sea, a dramatic regional widening of the Israel-Hamas war in Gaza.

In a statement after the strikes, Saudi Arabia called for restraint and "avoiding escalation". It said it was monitoring the situation with "great concern. The kingdom emphasises the importance of maintaining the security and stability of the Red Sea region, as the freedom of navigation in it is an international demand."

As witnesses in Yemen confirmed explosions throughout the country to Reuters, President Joe Biden cautioned in a statement late on Thursday he would not hesitate to take further action if needed.

"These targeted strikes are a clear message that the United States and our partners will not tolerate attacks on our personnel or allow hostile actors to imperil freedom of navigation," Biden said.

Britain's ministry of defence said in a statement that "early indications are that the Houthis' ability to threaten merchant shipping has taken a blow." Iran, which supports the Houthis, strongly condemned the attacks. A spokesperson for the Houthis said there was no justification for the attacks and that the group will continue targeting ships heading towards Israel.

Russia said it had requested an urgent meeting of the UN Security Council to discuss the military strikes.

The Houthis say their attacks on shipping routes in the Red Sea are a show of support for the Palestinians.

US Defence Secretary Lloyd Austin, who is in hospital due to surgery complications, said in a statement that the strikes targeted Houthi capabilities including drones, ballistic and cruise missiles, coastal radar and air surveillance.

A Houthi official confirmed "raids" in the capital Sanaa along with the cities of Saada and Dhamar and in Hodeidah governorate, calling them "American-Zionist-British aggression."

Witnesses told Reuters that the raids targeted a military base adjacent to Sanaa airport, a military site near Taiz airport, a Houthi naval base in Hodeidah and military sites in Hajjah governorate.

Fears of escalation

The US said Australia, Bahrain, Canada and the Netherlands supported the operation, and sought to present the strikes as part of an international effort to restore the free flow of trade in a key route between Europe and Asia that accounts for about 15 per cent of the world's shipping traffic.

But the strikes, the first on Yemeni territory since 2016, were also an undeniable demonstration of Washington's struggle to contain the fallout of the Gaza war in the Middle East since its eruption in October. Although Washington said there was no intent to escalate tension, the Houthis have vowed to retaliate to any attack.

"The concern is that this could escalate," said Andreas Krieg at King's College in London.

The United States also accused Iran of being involved operationally in the Houthi attacks in the Red Sea, providing the military capabilities and intelligence to carry them out.

The strikes were carried out by aircraft, ship and submarine. A different US official said more than a dozen locations were targeted and the strikes were intended to weaken the Houthis' military capabilities, as opposed to being just symbolic.

The Houthis, who control most of Yemen, defied UN and other international calls to halt their missile and drone attacks on Red Sea shipping routes and warnings from the United States of consequences if they failed to do so.

The Houthi attacks have disrupted international commerce, forcing international shipping to take the long route around South Africa to avoid being struck. The increase in delivery costs is stoking fears it could trigger a fresh bout of global inflation.

Reuters