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 Wednesday.
The decision comes after the US and Britain, with support from other nations, struck military targets of the group following Red Sea attacks.
The US government last week 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, 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 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.