On Wednesday, dozens of US troops left Chad after the country's military leaders raised concerns over their presence ahead of the 6 May elections.

Gen Michael Langley told the BBC it was a "temporary repositioning" of troops.

Last month, US troops left neighbouring Niger after being ordered out by the country's junta.

Russian military instructors have arrived in Niger as part of a new agreement with the military leaders.

Several other military-led countries in the Sahel region have also recently strengthened ties with Russia and cut them with France, the former colonial power, as they try to fight an Islamist insurgency in the region.

The Sahel region is considered the new global epicentre of the Islamic State group.

Gen Langley said that violent extremist organisations were the biggest threat to Africa's stability.

Last year, Niger and Burkina Faso both announced they were following Mali in withdrawing from the G5 international force set up to fight Islamists in the region. The three military-run countries have instead set up their own grouping - the Alliance of Sahel States.

The US set up a drone base in the central Niger city of Agadez, 750km (460 miles) north-east of the capital, Niamey, in 2016 to help monitor regional jihadist activity.

But in March after Niger ordered US troops to leave. Military spokesperson Col Amadou Abdramane accused the US of raising objections about the allies that Niger had chosen.

Col Abdramane condemned the US for its "condescending attitude" and "threat of reprisals".

But Gen Langley said that the "ultimate goal" of the US was to continue a dialogue with those countries that have been taken over by juntas.

He told the BBC the US hopes to get the juntas "on a roadmap back to democracy".

"That's the ultimate goal of the US government - of our continued engagement with these countries that have been taken over by juntas.

He said that he had spoken several Chadian leaders. "They are still inviting us in for continued relations because we've enjoyed a lot of success in helping Chad fight terrorism," he said.

"In Niger, our talks are still ongoing, whether we reset or reposition will just really be based on the threat, but also - every country we engage with is at the request of that country."