Yemen’s Houthi fighters say they have seized a UAE-flagged vessel in the Red Sea, claiming it carried “military supplies” after the Saudi-led coalition accused the armed group of “piracy”.

The vessel “entered Yemeni waters without authorisation” off the coast of Hodeidah and was carrying out “hostile acts”, the Houthi military spokesman Yahia Saree said on Twitter on Monday.

The seizure of the Rwabee marks the latest assault in the Red Sea, a crucial route for international trade and energy shipments.

First word of the Rwabee’s seizure came from the British military’s United Kingdom Maritime Trade Operations, which only said an attack targeted an unnamed vessel around midnight.

The coordinates it offered corresponded to the Emirati-flagged landing craft Rwabee, which had not given its location via satellite-tracking data for hours, according to the website MarineTraffic.com.

Hours later, a statement from the Saudi-led coalition, carried by state media in the kingdom, acknowledged the attack, saying the Houthis had committed an act of “armed piracy” involving the vessel.

The coalition asserted the ship carried medical equipment from a dismantled Saudi field hospital in the distant island of Socotra.

“The Houthi militia must immediately release the ship, otherwise the coalition forces shall take all necessary measures and procedures to deal with this violation, including the use of force,” Brigadier-General Turki al-Malki said in a statement on Monday.

The Houthis later aired footage from the Rwabee on their Al Masirah satellite news channel. It showed military-style inflatable rafts, trucks and other vehicles on the vessel, a landing craft that lowers a ramp to allow equipment to roll on and off. One brief clip showed what appeared to be a collection of rifles inside a container.

“It is completely obvious today that the information that this ship was carrying a civilian field hospital is not correct,” said Yahia Sare’e, a Houthi military spokesman. “This is clearly military equipment.”

Saudi state television alleged the Houthis transferred the weapons onto the ship.

In 2016, Emirati vessel SWIFT-1, which had been sailing back and forth in the Red Sea between an Emirati troop base in Eritrea and Yemen, was attacked by Houthi forces.

The Emirati government asserted that the SWIFT-1 carried humanitarian aid. UN experts later said of the claim that they were “unconvinced of its veracity”.

Yemen was plunged into chaos in 2014 when Houthi rebels seized control of the capital Sanaa. A coalition, led by Saudi Arabia, intervened in 2015 in support of the government.

During the conflict, which has killed tens of thousands and pushed Yemen to the brink of famine, the Saudi-led coalition has launched thousands of air raids inside Yemen that also hit markets, schools and hospitals. Houthi forces have regularly sent drones and fired missiles into Saudi Arabian cities.

Some four million people have been internally displaced during the fighting. In September, the World Food Programme warned that 16 million Yemenis were “marching towards starvation”.