Yemen’s Houthis said on Monday they have arrested an “American-Israeli spy cell,” a few days after the Iran-backed group detained about a dozen United Nations personnel.

The alleged cell included former staff members of the U.S. embassy in Yemen, according to a television statement from Abdel Hakim Al Khaiwani, the Houthis’ intelligence chief.

“The American-Israeli spy cell carried out espionage and sabotage activities in official and unofficial institutions for decades in favour of the enemy,” he said.

“Members of the spy spell and American officers exploited their positions at the American embassy to carry out their sabotage activities. After the American embassy left Sanaa ... the members of the spy cell continued to implement their sabotage agendas under the cover of international and UN organizations.”

Israeli government officials had no immediate comment, and the U.N. declined to comment on the allegations. The U.S. State Department did not immediately respond to a request for comment.

U.N. spokesperson Stephane Dujarric said the agency was working to secure the release of its 11 detained staff who work for five U.N. agencies and the U.N. envoy for Yemen.

In a series of raids, armed Houthi intelligence officers also detained three employees of the U.S.-funded pro-democracy group National Democratic Institute and three employees of a local human rights group, according to three officials of Yemen’s internationally recognized government who spoke to Reuters on Friday.

Houthi Al Masirah TV posted a series of videos on its Telegram channel allegedly showing the confessions of some of those arrested. Reuters could not independently verify the videos.

The Houthis, who are aligned with Iran, have attacked shipping in the Red Sea in what they say are acts of solidarity with Palestinians amid the Gaza war, drawing airstrikes from the United States and Britain.

They have held around 20 Yemeni employees of the U.S. embassy in Sanaa for the past three years. The embassy suspended operations in 2014.

Hatem Maher and Muhammad Al Gebaly reported from Cairo, and Mohammed Ghobari reported from in Aden.