ADEN - Yemen's Houthi authorities have ordered US and British staff of the United Nations and Sanaa-based humanitarian organisations to leave the country within a month, a document and a Houthi official said on Jan 24.

The decision comes after the United States and Britain, with support from other nations, struck military targets of the Iran-aligned group which has been launching attacks on commercial ships in the Red Sea that it says are linked to Israel.

The US government on Jan 17 also returned the group to a list of terrorist groups as Washington tries to stem attacks on international shipping in the Red Sea. The Houthis have said their attacks are in solidarity with the Palestinians as Israel strikes Gaza.

"The ministry... would like to stress that you must inform officials and workers with US and British citizenships to prepare to leave the country within 30 days," said a letter sent by the Houthi foreign ministry to the UN's acting humanitarian coordinator in Yemen, Mr Peter Hawkins.

The letter also ordered foreign organisations to not hire American and British citizens for Yemen's operations.

Houthi top negotiator Mohammed Abdulsalam confirmed the letter's authenticity to Reuters.

The office of Mr Hawkins, who is himself a British national, did not respond to a request for comment. The US and British embassies in Yemen did not immediately respond to a request for comment.

The Houthi movement controls much of Yemen after nearly a decade of war against a US-backed and Saudi-led coalition. The war has shifted to a no-war, no-peace stalemate as the fighting has largely stopped, but both parties have failed to formally renew a UN-brokered ceasefire.

US and British warplanes, ships and submarines have launched dozens of air strikes across Yemen in retaliation for Houthi attacks as container vessels have been forced to divert from the Red Sea, the fastest freight route from Asia to Europe.

US and British forces on Jan 23 targeted a Houthi underground storage site as well as missile and surveillance capabilities, the Pentagon said. REUTERS