According to two people familiar with the situation, at least 25 Yemenis working for the US in Sanaa have been detained in recent weeks by the Iran-backed Houthi militia that controls the capital.

According to the people who declined to be identified because they were not authorized to discuss the detentions, those rounded up include Yemenis working for the US embassy and USAID, the American government’s international development arm.

The reasons for the arrests, which occurred over the last three weeks, are unknown, but they coincide with the US and Saudi Arabia’s efforts to end the war in Yemen. The US embassy was closed in 2015.

Houthis took the capital, but some local staff continue to work from home or as security guards for the premises.

The US is extremely concerned by reports of detentions of some of its local Yemeni employees in Sanaa, said a spokesperson for the State Department.

The US calls on the Houthis to immediately release unharmed all employees and end any harassment of its staff, the spokesperson added.