Local rights groups in Mali warn that the army and its allies are torturing and killing civilians from an ethnic group accused of collaborating with Islamic militants in central Mali as concerns mount about the spread of extremism there.

There has been a "worrying spike in abuses by the army against suspected jihadists," the vast majority of whom are from the Peuhl ethnic group, said Corinne Dufka, West Africa associate director with Human Rights Watch.

"Witnesses and family members have described how men detained around Diabaly and Boni were severely beaten or burned and in three cases, subjected to enforced disappearance," she said. "These cases simply must be investigated."

At least eight civilians have been killed by soldiers or allied militias since the beginning of the year and three others have disappeared, according to Sekou Bah, secretary-general of a Malian group known as Dental Wuwarbe. Another rights group, Association of Peulhs, places the death toll higher, saying at least 15 have been killed.

"I can confirm that the army has arrested some Peuhls who are suspected jihadists but concerning the reports of disappearances and deaths, I am not aware of that," said Col. Diarran Kone, a spokesman for Mali's Defense Ministry. "The people speaking of these cases should provide us with proof of these allegations."

The reports come amid the rise of an extremist group in southern Mali known as the Macina Liberation Front, which is made up primarily of men who are Peuhl.

Northern Mali fell under the control of al-Qaida and other extremists in 2012. A French-led military offensive forced them from power the following year, but they have since regrouped to launch scores of attacks on peacekeepers and soldiers. Al-Qaida militants also carried out a major attack on a hotel in the capital late last year, killing 20 people.