Houthi rebels are holding 20 United Nations employees in Sanaa, including UNICEF's representative in Yemen, British national Peter Hawkins, UN officials announced Sunday.

The day before, rebels controlling Sanaa raided a UN building where the international organization's employees reside in the war-torn capital of Yemen.

"Five national staff members and 15 international staff members are being held in the UN compound," Jean Alam, spokesman for the UN resident coordinator in Yemen, told AFP.

According to him, 11 other Yemeni employees were released after being included and the UN is in contact with the Houthis and other parties to "resolve this serious situation as quickly as possible and end the detention of all staff."

"Peter Hawkins is one of 15 international employees detained at the compound," a UN official said on condition of anonymity. This information was confirmed to AFP by two Houthi security sources.

On Saturday, Mr. Alam told AFP that Houthi forces had entered the UN compound in Sanaa "without authorization."

The rebels already stormed UN offices in Sanaa on August 31, detaining around ten employees, according to the UN. They are suspected of spying for the United States and Israel, according to the senior Houthi official.

Dozens of UN staff have been arrested in recent months in areas controlled by Yemeni insurgents, backed by Iran.

In a televised address on Thursday, rebel leader Abdelmalek al-Houthi said his forces had dismantled "one of the most dangerous spy cells," which he said was "linked to humanitarian organizations such as the World Food Program and UNICEF."

The accusations were described on Saturday as "dangerous and unacceptable" by the spokesperson for the UN Secretary-General, Stéphane Dujarric, who said they "seriously endanger the safety of UN personnel and humanitarian workers, and compromise vital relief operations."

More than a decade of civil war has plunged Yemen, one of the poorest countries in the Arabian Peninsula, into one of the world's worst humanitarian crises, according to the UN.