NEW YORK: The United Nations has on Thursday rejected accusations by Yemen's Houthi authorities that UN staff were involved in espionage, calling the claims "extremely disturbing" and warning they put lives at risk.

“We categorically reject any and all accusations that UN personnel or UN operations in Yemen were involved in any form of espionage or in any activities that were not consistent with our humanitarian mandate,” said Stéphane Dujarric, spokesperson for UN Secretary-General António Guterres.

“Accusations, calling UN staff spies or, as we’ve seen in other contexts, calling them terrorists — all that does is it puts the lives of UN staff everywhere at risk, and it's unacceptable.”

Dujarric's comments came in response to a wave of detentions by Houthi authorities targeting UN and NGO workers in Yemen. At least 53 UN staff members remain arbitrarily detained, some held incommunicado for years, according to the UN.

The Houthi rebels have in recent weeks accused the UN of spying for the United States and Israel, exhibiting political bias, and failing to condemn Israeli military actions. These allegations emerged after an Israeli airstrike in September killed several senior Houthi officials in Sanaa.