WASHINGTON (AP) — Russia has moved some troops onto an airbase in Niger where a small number of U.S. forces remain after most American troops left the base in the nation’s capital, Niamey, a U.S. official said Thursday.

The arrival of Russian trainers in the West African country about three weeks ago came in the wake of Niger’s decision to order out all U.S. troops. The order dealt a blow to U.S. military operations in the Sahel, a vast region south of the Sahara desert where groups linked to al-Qaida and the Islamic State group operate.

The Pentagon has said the U.S. troops will depart but has not provided a precise timeline.

When Russian troops arrived last month, it wasn’t clear where they were staying. A U.S. official said they are now located on the other side of the Niamey facility, known as Airbase 101, and are not near U.S. forces. The base is by the Diori Hamani International Airport, where other international forces — such as the Germans and Italians — also reside.