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.

The official spoke on condition of anonymity to discuss troop movements. It’s not clear exactly how many U.S. troops remain at the Niamey base.

The Russian presence on the base comes as tensions remain high between Washington and Moscow over the ongoing U.S. support for Ukraine’s military.

About 1,000 U.S. troops are still in Niger, but the bulk of them moved to what’s called Airbase 201 near Agadez, some 920 kilometers (550 miles) away from the capital, not long after mutinous soldiers ousted the country’s democratically elected president last July.

A few months later, the ruling junta asked French forces to leave and turned to the Russian mercenary group Wagner for security assistance.

In October, Washington officially designated the military takeover as a coup, which triggered U.S. laws restricting the military support and aid that it can provide to Niger. Since then, diplomatic efforts to restore ties with Niger have been unsuccessful.

Until recently, Washington considered Niger a key partner and ally in a region swept by coups in recent years, investing millions of dollars in the Agadez base, which has been critical to U.S. counterterrorism operations in the Sahel. The U.S. also has invested hundreds of millions of dollars in training Niger’s military since it began operations there in 2013.

The Pentagon also has said the U.S. will relocate most of the approximately 100 forces it has deployed in neighboring Chad for now. Chad is also considering whether to continue its security agreement with the U.S.

Maj. Gen. Pat Ryder, Pentagon press secretary, told reporters that the departure from Chad “is a temporary step as part of the ongoing review of our security cooperation, which will resume after Chad’s May 6th presidential election.”

(AP)