The US secretary of defence, Lloyd Austin, has confirmed Russian security forces have been deployed to the same airbase as American troops in the Nigerien capital, Niamey.

It remains unclear when the Russian troops, who have been in Niger for weeks, were deployed to Airbase 101, which is next to Diori Hamani international airport in Niamey. It is also unclear how many troops are on the ground.

“Airbase 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,” Austin said at a press conference in Honolulu.

In response to news of the deployment, the Kremlin spokesperson, Dmitry Peskov, told reporters in Moscow on Friday that Russia was “developing ties with various African countries in all areas, including in the military one”.

The development is the latest fallout from a coup in July last year that deposed the democratically elected president, Mohamed Bazoum. Niger’s junta has since embarked on a reconfiguration of its partnerships with western allies. Troops from the US and France, which has a strained relationship with many countries in the region, most of them being its former colonies, have been asked to leave their bases.

Russia is continuing to make inroads into parts of the continent, reawakening cold war-era relations in recent years and in some cases presenting “regime stabilisation” packages to African leaders. The face of Moscow’s presence has mostly been the Wagner mercenary group.

Ikemesit Effiong, the head of research at Lagos-based geopolitical risk advisory SBM Intelligence, said the presence of Russian and US troops in the same Nigerien base is evidence that the region is now “a live geopolitical faultline, with a pro-western coastal West Africa and a Russophile Sahel”.

“With the fraying of democracy and stressed economies within the region, countries will fall in and out of both blocs with a frequency that will keep Washington and Moscow busy for years to come,” he added.

After the coup, the US military moved some of its forces in Niger from Airbase 101 to Airbase 201 in the city of Agadez. It is not clear what US military equipment remains at Airbase 101.

The US built Airbase 201 in central Niger at a cost of more than £80m. Since 2018, it has been used to target Islamic State and the al-Qaida affiliate Jama’at Nusrat al-Islam wal Muslimeen with drones.

Washington is concerned about jihadists in the Sahel region possibly expanding their sphere of influence without western-led counterinsurgency activity, especially in intelligence.

Niger’s move to ask for the removal of US troops came after a meeting in Niamey in mid-March, when senior US officials raised concerns including about the expected arrival of Russian forces and reports of Iran seeking raw materials in the country, including uranium.