Friends and former colleagues of Shaif al-Hamdani did not know if they would ever see him again.

A Yemeni former employee of the U.S. Embassy in his country, Mr. al-Hamdani had been arrested in 2021 by Houthi militants who had taken control of the capital, Sana. In the years that followed, little was known about his case or those of 10 other active or former Yemeni employees of the U.S. Embassy detained with him, except that they were being held for links to the United States.

Then in June, Mr. al-Hamdani reappeared in a most distressing way: In a propaganda video released by the Houthis, he confessed to spying for the United States and Israel.

“Seeing Shaif in that blue prison jumpsuit, forced to confess under duress, it broke my heart,” said Adam Ereli, an American diplomat who worked with Mr. al-Hamdani at the embassy more than two decades ago.

The video was released in early June a few days after the Houthis — an Iran-backed militia that now controls most of northern Yemen — made a new series of arrests. They rounded up at least 27 staff members of United Nations agencies or local and international humanitarian organizations. In the following weeks, dozens more Yemenis working for similar groups were detained.

That wave of arrests in June raised fears of a broader crackdown on those linked to international organizations and foreign missions in Yemen. Tensions between the Houthis and the West have heightened over the past year, as the Yemeni militants have attacked international shipping in the Red Sea and the Gulf of Aden and fired missiles at Israel in solidarity with the Palestinians in Gaza.

Nadwa al-Dawsari, a conflict analyst, said Houthi repression and detentions of U.N. and international staff had been going on for at least five years. But she suggested the newest round of arrests had a more focused goal: stifling local support for Western powers and institutions.