Houthi rebels say at least 18 civilians were killed after US President Donald Trump ordered a series of airstrikes on Saturday on the group’s stronghold areas in Yemen.

Trump threatened to use “overwhelming lethal force” until the Iran-backed group ceases its attacks on shipping along a vital maritime corridor.

“Our brave war fighters are right now carrying out aerial attacks on the terrorists’ bases, leaders, and missile defences to protect American shipping, air, and naval assets, and to restore Navigational Freedom,” Trump said in a post on his platform, Truth Social.

“No terrorist force will stop American commercial and naval vessels from freely sailing the Waterways of the World.”

The US President also warned Iran to stop supporting the rebel group, promising to hold the country “fully accountable” for the actions of its proxies in the region.

The development comes two weeks after Trump sent a letter to Iranian leaders offering a path to restarting bilateral talks between the countries on Tehran’s rapidly advancing nuclear programme. Trump says he will not allow Tehran’s programme to become operational.

The Houthis reported explosion on their territories, particularly the capital, Sanaa, and the northern province of Saada, the rebels’ stronghold on the border with Saudi Arabia.

Images online showed plumes of black smoke over the area of the Sanaa airport complex, which includes a sprawling military facility. The Houthis also reported airstrikes early Sunday on the provinces of Hodeida, Bayda, and Marib.

At least 18 people were killed, including 13 in Sanaa and five in Saada, according to the Houthi-run health ministry. At least 24 others were wounded, including nine in Sanaa and 15 in Saada, it said.

Nasruddin Amer, deputy head of the Houthi media office, said the airstrikes won’t deter them and they would retaliate against the U.S.

“Sanaa will remain Gaza’s shield and support and will not abandon it no matter the challenges,” he added on social media.

The airstrikes come days after the Houthis said they would resume attacks on Israeli vessels sailing off Yemen in response to Israel’s latest blockade on Gaza. They described the warning as affecting the Red Sea, the Gulf of Aden, the Bab al-Mandeb Strait and the Arabian Sea.

There have been no Houthi attacks reported since then.

The Houthis had targeted over 100 merchant vessels with missiles and drones, sinking two vessels and killing four sailors, during their campaign targeting military and civilian ships between the start of the war between Israel and Hamas in late 2023 and January of this year, when this ceasefire in Gaza took effect.

The attacks raised the Houthis’ profile as they faced economic and other problems at home amid Yemen’s decade-long stalemated war that’s torn apart the Arab world’s poorest nation.