The Mine Resistant Ambush Protected All-Terrain Vehicle activated the bomb "while entering a firing range in the vicinity of Ouallam, Niger on June 8, 2019" during a joint training exercise, US Africa Command said in a statement.

"There are no reported US casualties, however, as a precaution, US service members are being evaluated," it said, adding that Nigerien forces had secured the scene of the blast.

Four American soldiers and four Nigerien soldiers were killed in an October 2017 ambush in the country, when scores of jihadists overran their convoy in southwestern Niger, near the border with Mali.

The ambush claimed the largest number of American lives in combat anywhere in sub-Saharan Africa since the "Black Hawk Down" incident in Somalia in 1993.

Niger is one of a number of poor, fragile countries in the Sahel region that have been hit by a jihadist revolt.

Various insurgent groups operate in the country's west and north, and Nigeria's Boko Haram is present in its southeast.

The country is part of the so-called G5 Sahel group set up to manage a coordinated response to the jihadist insurgency.