The top U.S. general is making a rare trip to Africa to discuss ways to preserve some of the U.S. presence in West Africa after Niger decided to kick out the U.S. military in favour of partnering with Russia in a major setback for Washington.

Air Force General C.Q. Brown, chairman of the Joint Chiefs of Staff, told reporters before landing in Botswana on Monday for a gathering of African chiefs of defence that he was going to speak with several partners in the region.

"I do see some opportunities. And there are countries that we're already working with in West Africa," Brown told reporters travelling with him.

Building on those relationships may "provide opportunities for us to posture some of the capability we had in Niger in some other locations," he added.

Brown declined to say which countries were under consideration. But a U.S. official told Reuters that President Joe Biden's administration has had initial conversations with countries including Benin, Ivory Coast and Ghana.

Still, the U.S. military is not expected to be able to replicate its muscular counter-terrorism footprint in Niger anytime soon. In particular, its ejection means losing Air Base 201, which the U.S. built near Agadez in central Niger at a cost of more than $100 million.

Until Niger's military coup last year, the base had been key to the U.S. and Niger's shared fight against insurgents who have killed thousands of people and displaced millions more.

A second U.S. official, also speaking on condition of anonymity, said not to expect another big U.S. base or wholesale relocation of U.S. troops from Niger to somewhere else.

"We do not expect a large military construction announcement or a significant new base to appear anywhere," the second official said.

POLITICAL UPHEAVAL

The changing political landscape in West and Central Africa presents a dilemma for the United States. The region has seen eight coups over four years, including in Niger and its neighbours Burkina Faso and Mali.

The juntas now ruling many of those countries are less willing to work with Western countries including the United States - whose military is legally barred from supporting governments that seized power through coup. They are increasingly looking to Russia, which faces no such constraints.

"The U.S. had solid partners in the region," said Catherine Nzuki at the Washington-based Center for Strategic and International Studies.

"And now that the U.S. has been pushed out of Niger, the political question that I think the Department of State is asking, the Department of Defense is asking, is: Are we losing allies in the region? Are things changing too rapidly for us to keep up?"

The second U.S. official acknowledged that the U.S. military was taking stock of the rapid changes.

"We are doing some introspection right now and thinking about what our modified goals should be," the official said.

The extent to which America's modified goals will allow it to address the threat from Islamist groups expanding across the arid, impoverished Sahel region remains unclear.

"The terrorist threat is alarming," the second official said.

So far, the U.S. withdrawal from Niger is being completed on schedule ahead of a Sept. 15 deadline, U.S. officials say, with only about 600 troops remaining at Air Base 101, which is next to Diori Hamani International Airport in the capital Niamey.

As the U.S. exits, Russia has deployed a number of military forces to the same base, where they are carrying out training activities. U.S. officials say U.S. and Russian troops have no contact with each other.

Brown held out hope that even after the U.S. withdraws there might be a way to maintain some kind of future security relationship with Niger, given the years-long investment in military ties.

"We have an embassy there, so we still have relationships. And so I don't know if the door is completely closed," Brown said. "And so if in the future, if the opportunity presents itself to rebuilt, re-strengthen the relationship, we'll work with the rest of the USG (U.S. government) to figure out how best to do that."