Any attack on Yemen’s Houthis on the part of the United States will not go without a response, the group’s leader Abdel-Malik al-Houthi has said in a televised speech, as the Iranian-backed group stepped up attacks on commercial vessels in the Red Sea in protest against Israel’s war in Gaza.

“Any American attack will not remain without a response. The response will be greater than the attack that was carried out with 20 drones and a number of missiles,” the Houthi leader said, referring to a strike on Wednesday, when Houthi drones and missiles targeted US and United Kingdom ships in the largest single attack yet on foreign vessels.

“We are more determined to target ships linked to Israel, and we will not back down from that,” al-Houthi said.

The comments come after the US and 11 allies published a joint statement last week calling for an end to Houthi attacks from Yemen on Red Sea shipping, sending out an implicit threat of force.

Various shipping lines have suspended operations, instead taking the longer journey around Africa. The Cyprus Shipping Chamber (CSC), a key shipping industry group representing around 200 companies in Cyprus and abroad, said the attacks could have a “substantial” impact on economies and a knock-on effect on prices around the world.

“Where countries heavily depend on raw materials, gas, grain, [and] pharmaceuticals, we will have to assume that it will have a substantial impact on day-to-day living, business operations, and this will have a multiplying effect,” CSC Director Thomas Kazakos said.

The Houthi movement, an Iran-aligned group that controls much of Yemen after nearly a decade of war against a Western-backed and Saudi-led coalition, has emerged as a strong supporter of the Palestinian group Hamas in its war against Israel.

The Houthis have attacked commercial ships they say are linked to Israel or bound for Israeli ports and have engaged directly with the US Navy in the Red Sea, firing ballistic missiles and deploying armed drones against US and UK warships.

Human Rights Watch, among other organisations, said attacks targeting civilians and civilian objects, if carried out deliberately or recklessly, would be a war crime. The rights watchdog argued that on more than one occasion, the targeted vessels presented no direct links to Israel or evidence of military targets on board.

The United Nations Security Council on Wednesday passed a resolution demanding the Houthis end attacks on ships in the Red Sea and free the Japanese-operated Galaxy Leader that was seized last year.

US-allied Gulf and Arab states, including Saudi Arabia, have been pressing Washington for an immediate ceasefire in Gaza, saying that is the only way to prevent the conflict from spreading beyond the Gaza Strip.

In an interview with Reuters on Thursday, the chief negotiator for Yemen’s Houthis said the group’s attacks on commercial ships in the Red Sea do not threaten its peace talks with Saudi Arabia, blaming Israel’s war on Gaza for dragging the Middle East into more regional conflict.

“It has nothing to do with what is happening in the Gaza Strip, unless the Americans want to move other countries in the region to defend Israel which is another matter,” Mohammed Abdulsalam told Reuters.

“The one who is dragging the region into a wider war is the one who allows the continuation of the aggression and the siege that continues for more than 100 days in the Gaza Strip.”

The group is seeking to pressure the Israelis and Americans into a ceasefire, including lifting the siege on Gaza and moving towards peace and dialogue, Abdulsalam added.

US forces have also been increasingly attacked in Iraq and Syria in the aftermath of Israel’s now three-month-old offensive into Gaza, launched in response to the October 7 attack on Israel by Hamas.