The decision follows strikes by the United States
and Britain, with support from other nations, against military targets of the 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 Houthis 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 bombards 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 US embassy said
in a statement it was aware of reports about the letter but "cannot speak
on behalf of the UN or humanitarian organizations in Yemen as to what they may
have received from Houthi 'authorities'".
The British embassy
said staff had not yet been told to leave and the mission was in close contact
with the UN on the issue.
"The UN
provide vital assistance to the Yemeni people ... via the very sea routes that
the Houthis are jeopardizing," the British mission in Yemen said in a
statement. "Nothing should be done that hinders their ability to
deliver," it added.
The Houthi movement
controls much of Yemen after nearly a decade of war against a US-backed
coalition. The war has shifted to a no-war, no-peace stalemate as the fighting
has largely stopped, but both parties have failed to renew formally 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 Tuesday targeted a Houthi underground storage site as well
as missile and surveillance capabilities, the Pentagon said.
