Russian military personnel have entered an air base in Niger that is hosting U.S. troops, a senior U.S. defense official told Reuters, a move that follows a decision by Niger's junta to expel U.S. forces.

The military officers ruling the West African nation have told the U.S. to withdraw its nearly 1,000 military personnel from the country, which until a coup last year had been a key partner for Washington's fight against insurgents who have killed thousands of people and displaced millions more.

A senior U.S. defense official, speaking on condition of anonymity, said Russian forces were not mingling with U.S. troops but were using a separate hangar at Airbase 101, which is next to Diori Hamani International Airport in Niamey, Niger's capital.

The move by Russia's military, which Reuters was the first to report, puts U.S. and Russian troops in close proximity at a time when the nations' military and diplomatic rivalry is increasingly acrimonious over the conflict in Ukraine.

It also raises questions about the fate of U.S. installations in the country following a withdrawal.
"(The situation) is not great but in the short-term manageable," the official said.

Asked about the Reuters report, U.S. Defense Secretary Lloyd Austin played down any risk to American troops or the chance that Russian troops might get close to U.S. military hardware.

"The Russians are in a separate compound and don't have access to U.S. forces or access to our equipment," Austin told a press conference in Honolulu.