UNITED NATIONS (AP) — The United Nations chief called on Yemen’s Houthi rebels on Tuesday not to prosecute detained U.N. personnel and to work “in good faith” to immediately release all detained staff from the U.N. and foreign agencies and missions.

Secretary-General Antonio Guterres condemned the referrals of the U.N. personnel to the Houthis' special criminal court and called the detentions of U.N. staff a violation of international law, U.N. spokesman Stephane Dujarric said.

There are currently 59 U.N. personnel, all Yemeni nationals, detained by the Iranian-backed Houthis, in addition to dozens from nongovernmental organizations, civil society and diplomatic missions, he said.

He said a number of them have been referred to the criminal court in Yemen’s capital, Sanaa. “There were procedures going on in the court, I believe, today and all of this is very, very worrying to us,” Dujarric said.

The court in late November convicted 17 people of spying for foreign governments, part of a yearslong Houthi crackdown on Yemeni staffers working for foreign organizations.

The court said the 17 people were part of “espionage cells within a spy network affiliated with the American, Israeli and Saudi intelligence,” according to the Houthi-run SABA news agency. They were sentenced to death by firing squad in public, but a lawyer for some of them said the sentence can be appealed.

U.N. human rights chief Volker Türk said in a statement Tuesday that one of those referred to the court was from his office. He said the colleague, who has been detained since November 2021, was presented to the “so-called” court “on fabricated charges of espionage connected to his work.”

“This is totally unacceptable and a grave human rights violence,” Türk said.

He said detainees have been held in “intolerable conditions” and his office has received “very concerning reports of mistreatment of numerous staff.” Dujarric said some have been held incommunicado for years.

Dujarric said the U.N. is in constant contact with the Houthis, and the secretary-general and others have also raised the issue of the detainees with Iran, Saudi Arabia, Oman and others.

The Houthis seized Sanaa in 2014 and since then they have been engaged in a civil war with Yemen’s internationally recognized government, which is supported by a Saudi-led military coalition.

The November verdict was the latest in the Houthi crackdown in areas of Yemen under their control. They have imprisoned thousands of people during the civil war.