Death toll from attack on Niger villages soars to 137

The unidentified assailants struck in the afternoon, raiding three villages and other hamlets in Tahoua region bordering Mali, the government said on Monday, revising the toll up from a previous estimate by local authorities of about 60 killed.

"By systematically targeting civilians, these armed bandits are reaching a new level of horror and savagery," it said in a statement, announcing three days of national mourning.

It did not say who authorities believed was behind the attacks. A security source earlier blamed ISIS, whose local affiliate is active in the zone.

The violence is part of a wider security crisis across West Africa's Sahel region, which is also fuelled by militants and ethnic militias.

The attacks on Sunday might have been revenge for the recent arrests of people suspected of belonging to armed groups in the area, said a report by the cluster of humanitarian organizations led by the U.N. Refugee Agency (UNHCR).