The UN's office in Yemen said yesterday that 20 of its staff were still being detained by Houthi rebels following a raid on their building in Sanaa the day before.

On Saturday, the UN office had said Houthi security forces had made an "unauthorised entry" into their compound, adding the staff there were "safe and accounted for".

"Five national staff and fifteen international staff remain detained within the compound," Jean Alam, spokesman for the UN resident coordinator, said yesterday.

"The United Nations is in contact with the authorities in Sanaa and with relevant Member States and the Government of Yemen to resolve this serious situation as swiftly as possible, end the detention of all personnel, and restore full control over its facilities in Sanaa."

The rebels had already stormed UN offices in Sanaa on August 31, detaining more than 11 employees, according to the UN. Those employees were suspected of spying for the United States and Israel, a senior Houthi official told AFP at the time on condition of anonymity.

In a statement on Saturday, UN Secretary-General Stephane Dujarric's spokesperson said: "We will continue to call for an end to the arbitrary detention of 53 of our colleagues."

He was responding to a televised address on Thursday by rebel leader Abdelmalek al-Houthi, during which he claimed his forces had dismantled "one of the most dangerous spy cells," which he said was "linked to humanitarian organisations such as the World Food Program and Unicef".