Niger's junta, which seized power last July, said in March it was ending a military cooperation agreement with Washington, which has agreed to withdraw its troops and sent a delegation to Niamey to work out an orderly departure.

Prior to the 2023 coup, Niger was a linchpin of US strategy to combat jihadists in West Africa, housing a $100 million American drone base and roughly 1,000 US troops.

The Russian deployment to Air base 101 in the capital Niamey puts Russian and American soldiers in close quarters at a time when Washington and Moscow are fiercely at odds over the war in Ukraine.

Asked about it at a news conference on Thursday, Austin said the Russian deployment did not pose a "significant issue... in terms of our force protection."

"Air base 101 where our forces [are], is a Nigerien air force base that is co-located with an international airport in the capital city. The Russians are in a separate compound and don't have access to US forces or access to our equipment," he said at a news conference in Hawaii.

At a briefing in Moscow, Kremlin spokesman Dmitry Peskov did not confirm or deny reports of the Russian presence at the Niger base, saying only that Moscow was cultivating ties with African countries in all areas including defense.

Following the overthrow of elected president Mohamed Bazoum, Niger's junta kicked out soldiers from former colonial power France.

Russian military instructors arrived in Niger last month with an air defense system and other equipment, Nigerien state media reported, after talks between military ruler General Abdourahamane Tiani and Russian President Vladimir Putin.

The US pullout would mark a new regional gain for Russia, which has ramped up its focus on Africa, backing military regimes in neighboring Mali and Burkina Faso.

Niger faces violence by Boko Haram jihadists and militants from the Islamic State West Africa Province in the southeastern region of Diffa near Nigeria.