President Joe Biden has said US military strikes against Iranian-backed Houthi rebels in Yemen will continue, but he acknowledged that the American and British bombardment has yet to stop the militants’ attacks on vessels in the Red Sea that have affected global shipping.

A US official said the United States conducted a fifth strike on Thursday morning that targeted another missile launcher site.

Mr Biden said the US would continue the strikes in an exchange with reporters before departing the White House for a domestic policy speech in North Carolina.

“When you say working, are they stopping the Houthis, no. Are they going to continue, yes,” the president said.

The US military fired another wave of ship and submarine-launch missile strikes against Houthi-controlled sites on Wednesday, marking the fourth time in days it has directly targeted the group in Yemen as violence that ignited in the wake of the Israel-Hamas war continues to spill over in the Middle East.

The strikes were launched from the Red Sea and hit 14 missiles that the command deemed an “imminent threat”.

They followed an official announcement on Wednesday that the US has put the Houthis back on its list of specially designated global terrorists.

The sanctions that come with the formal designation are meant to sever violent extremist groups from their sources of financing, while also allowing vital humanitarian aid to continue flowing to impoverished Yemenis.

Despite sanctions and military strikes, including a large-scale operation carried out by US and British warships and warplanes that hit more than 60 targets across Yemen, the Houthis keep harassing commercial and military ships.

The US has strongly warned Iran to cease providing weapons to the Houthis.

For months, the Houthis have claimed attacks on ships in the Red Sea that they say are either linked to Israel or heading to Israeli ports.

They say their attacks aim to end the Israeli air-and-ground offensive in the Gaza Strip that was triggered by the Palestinian militant group Hamas’s October 7 attack in southern Israel.

However, the links to the ships targeted in the rebel assaults have grown more tenuous as the attacks continue.

The attacks have targeted commercial shipping vessels transiting through the critical Bab el-Mandeb Strait that links markets in Asia and Europe since the October 7 attack by Hamas and Israel’s subsequent war against the militant group in Gaza.

Separately, the US and its allies have formed Operation Prosperity Guardian to protect ship traffic, and currently warships from the United States, France and the United Kingdom are patrolling the area.

“These strikes will continue for as long as they need to continue,” National Security Council spokesman John Kirby said on Thursday, adding: “I’m not going to telegraph punches one way or another.”

The comments came on the same day that the Houthi rebels’ supreme leader vowed that attacks by his forces on ships in the Red Sea and the Gulf of Aden will continue.

“We will continue targeting ships linked to Israel,” Abdel Malek al-Houthi said in an hour-long televised speech, and later added the Houthi operations would “also include American and British ships”.

He also said his forces will continue to develop their military capabilities and that recent air strikes by the United States and United Kingdom on Houthi targets do “not scare us”.

Thursday’s speech is al-Houthi’s first public address since the US and UK strikes last week.