In a report, the rights group suggested the alleged massacre perpetrated over four days, in the town of Moura in volatile central Mali, was a war crime.

Malian soldiers and white foreign fighters arrived in the town by helicopter on March 27 and exchanged fire with about 30 Islamist fighters, several witnesses told Human Rights Watch (HRW). Some jihadists then attempted to blend in with the local population.

Over the ensuing days, Malian and foreign fighters allegedly rounded people up and executed them in small groups.

HRW estimated that about 300 people were killed in total, with the vast majority of the victims being ethnic Fulanis.

"The incident is the worst single atrocity reported in Mali's decade-long armed conflict," the report said.

Mali's army said on Friday that it killed 203 militants in Moura. However, that announcement followed widely shared social media reports of a civilian massacre in the area.

The United States, European Union, United Nations and Mali's former colonial power France have all raised concerns about the possible killing of civilians in Moura.

AFP was unable to independently confirm the Malian armed forces' account or the social media reports.

HRW's recent report attests to fears of a mass civilian killing in Moura, however.

The study was based on interviews with 27 people, including witnesses from the Moura area, foreign diplomats and security analysts, the rights group said.

"The Malian government is responsible for this atrocity, the worst in Mali in a decade, whether carried about by Malian forces or associated foreign soldiers," said HRW Sahel Director Corinne Dufka, who urged an investigation.

Several witnesses and other sources identified the foreign soldiers as Russians to HRW.

Russia has supplied what are officially described as military instructors to Mali, an impoverished country that has been battling a brutal jihadist conflict since 2012.

However, the United States, France, and others, say the instructors are operatives from the Russian private-security firm Wagner.

Mali's ruling military, which seized power in a coup in August 2020, denies the allegation. It also routinely defends the rights record of the armed forces.