Suspected jihadists killed 40 Tuaregs, most of whom were young men, in two attacks in northern Mali's Menaka region, according to the local governor, Daouda Maiga.
She said the attacks seemed calculated to spark an ethnic conflict between Tuareg and Fulani herders.
Maiga told Reuters that the attacks happened in the remote desert villages of Awakassa on Friday and in Anderanboucane on Thursday.
Bajan Ag Hamatou, a local legislator, confirmed the attack, as did Menaka town's mayor, Nanout Kotia.
Jihadist groups pose a threat to security across Africa's Sahel region, exploiting tensions between ethnic groups in an area.
For example, the Tuareg, historically nomadic Berber people, and Fulani herdsmen's enmity over scarce watering points in the Sahara.
Mali has been in chaos since Tuareg rebels and Islamists swept across its deserts in 2012, despite a French intervention to push them back the following year, and a large French military and UN peacekeeping presence.
Increasing violence across the country has cast doubt over the possibility of upcoming elections in July, where President Ibrahim Boubacar Keita will seek a second term.