The Sudanese government is sending more troops to the restive Darfur region, following a spike in violence there.
Prime Minister Abdalla Hamdok said the forces would protect people during the farming season.
Unidentified gunmen killed more than 60 people in the region on Saturday, and another 20 the day before, the UN said.
Hundreds of thousands of people have died in fighting between government forces and rebels since 2003. Millions have been forced from their homes.
In the latest upsurge, several villages were burned, and markets and shops looted, said the UN Office for the Co-ordination of Humanitarian Affairs (OCHA).
"The escalation of violence in different parts of Darfur region is leading to increased displacement, compromising the agricultural season, causing loss of lives and livelihoods and driving growing humanitarian needs," it said in a statement.
No group has so far said it carried out the attacks.
Former President Omar al-Bashir, who was overthrown last year, is wanted by the International Criminal Court (ICC) for alleged war crimes and genocide in the region.