The toll is one of the bloodiest in Mali's decade-long insurgency, which has spread from the north of the country to the centre and south and into neighbouring Burkina Faso and Niger.

The document was authenticated to AFP by several senior military officials.

The attack occurred on Sunday in the town of Tessit, in the troubled "three-border" region where the frontiers of the three nations converge.

On Monday, the army had said 17 soldiers and four civilians had died. Relatives of the victims, speaking on condition of anonymity, said that some of the civilians had been elected officials.

Monday's statement also said that seven attackers had died, "probably members of the Islamic State in the Greater Sahara (ISGS) and benefiting from drone and artillery support and using explosives and an explosives-laden vehicle."

Tessit and its nearby military base have been repeatedly attacked.

In March 2021, 33 soldiers were killed in an ISGS ambush as units were being rotated.

The insurgency that has swept the three Sahel countries has claimed thousands of lives and forced more than two million to flee their homes.

Sporadic cross-border attacks have also occurred in Ivory Coast, Togo and Benin to the south, amplifying fears of a jihadist push towards the Gulf of Guinea.