CAIRO (AP) — Iranian-backed Houthi rebels detained two dozen U.N. employees Sunday, a day after they raided another U.N. facility in the capital Sanaa, a U.N. official said.

Jean Alam, a spokesman for the U.N. resident coordinator for Yemen, told The Associated Press that the U.N. staffers were detained inside the facility in Sanaa’s southwestern neighborhood of Hada.

He said those detained Sunday include five Yemenis and 15 international staff. He said the rebels released another 11 U.N. staffers after questioning.

He said the U.N. was contact with the Houthis and other parties to “to resolve this serious situation as swiftly as possible, end the detention of all personnel, and restore full control over its facilities in Sanaa.”

A second U.N. official, speaking on condition of anonymity to discuss the raid, said the rebels confiscated all communications equipment from the facility, including phones, servers and computers.

The official said the detained employees belong to multiple U.N. agencies including the World Food Program, UNICEF and the Office for the Coordination of Humanitarian Affairs.

The Houthis have launched a long-running crackdown against the U.N. and other international organizations working in rebel-held areas in Yemen including Sanaa, the coastal city of Hodeida and the rebel stronghold in Sadaa province in northern Yemen.

Dozens of people, including over 50 U.N. staffers, have been detained so far. A World Food Program worker died in detention earlier this year in Sadaa.

The rebels have repeatedly alleged without evidence that the detained U.N. staffers and those working with other international groups and foreign embassies were spies. The U.N. fiercely denied the accusations.

The crackdown forced the U.N. to suspend its operations in Saada province in northern Yemen following the detention of eight staffers in January. The U.N. also relocated its top humanitarian coordinator in Yemen from Sanaa to the coastal city of Aden, which serves as seat for the internationally recognized government.