"The attack started last night and, as information is still coming through, I am outraged to hear the premises of several aid agencies and a hospital were reportedly set ablaze or sustained damage," the UN's humanitarian coordinator in Nigeria, Edward Kallon, said in a statement.

"This violent attack will affect the support provided to nearly 100,000 people who are desperately in need of humanitarian assistance and protection," he said.

The Islamic State West Africa Province (ISWAP) group, which split from mainstream Boko Haram in 2016, is suspected to be behind the attack.

The government and the army have yet to comment.

President Muhammadu Buhari reshuffled the military command this year, raising hopes of a shift in strategy to end a 12-year-old conflict that has killed 36,000 people and forced around two million to flee their homes.