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.