BAMAKO, Aug 9 (Reuters) - At least 51 people were killed when Islamist militants raided three villages in central Mali near the border with Niger, a district administrator said on Monday. Ouatagouna, Karou and Deouteguef were simultaneously attacked around 6 p.m. on Sunday, according to a note from the Asongo district administrator to the governor of Gao region. The United Nations mission in Mali said it would deploy additional troops to secure areas where the attacks took place and intensify existing patrols. Houses were ransacked and burned to the ground and herds of livestock carried away, said the administrator"s note, which was seen by Reuters. "Provisional toll is 51 killed, several other injured," it said. No group has yet taken responsibility for the attacks in the area where Malian troops, French and European forces, and U.N. peacekeepers have been battling insurgents linked to Islamic State and al Qaeda. "These deliberate attacks against civilian populations constitute serious violations of international human rights law and international humanitarian law," the U.N. statement said. "They are liable to be classified as crimes against humanity." Local sources told Reuters that militants stationed themselves at the towns" entrances and fired indiscriminately upon civilians. The administrator said Malian troops where sweeping the area. He also requested a military escort to "help with the funerals, reassure the populations and offer condolences to the bereaved families", according to the note. Mali"s army spokesman Colonel Souleymane Dembele confirmed the attacks but gave no further details. Former colonial power France announced in June that it would end its eight-year military operation in Mali, which sought to drive back al Qaeda-linked groups, instead committing troops to broader international efforts in the region.