Yemen’s Houthi authorities have ordered US and British staff of the UN and Sanaa-based humanitarian organisations to leave the country within a month, a document and a Houthi official said on Wednesday.

The decision follows the US and Britain, with support from other nations, striking military targets of the Iran-aligned group which has been launching attacks on commercial ships in the Red Sea that is says are linked to Israel.

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 UK national, did not respond to a request for comment. The US and British embassies in Yemen did not respond to a request for comment.