The UN mission in the country said in a statement that human rights investigators had uncovered evidence of forced disappearances, kidnapping and robbery around the strategic city of Kidal.

The investigators further uncovered "the existence of individual tombs and mass graves" in the town of Anefis, the statement added, but warned they were not "able to establish at this stage the number of people buried or the circumstances of their deaths".

The UN also raised fears of the "possible presence" of child soldiers among the ranks of both armed groups, which if confirmed would "constitute serious children's rights violations at a time of armed conflict."

Northern Mali is the site of frequent clashes between the rival armed groups, as well as a haven for jihadist activity, though fighting between Platform and CMA combatants has intensified in recent weeks.

Sources told AFP in late July that "dozens" of members of the GATIA militia were killed in clashes monitored by a UN helicopter that later crashed accidentally, killing two German crew.