The United Nations on Tuesday said it was "outraged" over an attack by suspected jihadists linked to the Islamic State group in northeast Nigeria that "directly targeted" aid facilities.
Scores of Islamic State West Africa Province (ISWAP) fighters invaded the town of Dikwa in the restive Borno state, dislodging troops from the military base, torching the humanitarian hub and trapping 25 aid workers, security and humanitarian sources told AFP a day earlier.
Military reinforcements, including fighter jets and a helicopter gunship, had been deployed to help repel the attackers, the military source said.
"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.
A spokesman for UN chief Antonio Guterres confirmed only that there was a "security incident", but gave no further details.
For more than a decade, Nigeria's military has battled an insurgency by the Islamist group Boko Haram that has devastated the northeast, killing at least 36,000 people and displacing more than two million.
The ISWAP group split from Boko Haram in 2016 and has become a dominant threat in the region, attacking soldiers and bases while killing and kidnapping passengers at bogus checkpoints.
The violence has spread into neighbouring Niger, Chad and Cameroon, prompting a regional military coalition to fight the militants.
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.
The latest assault in Dikwa comes three years to the day after ISWAP fighters attacked a UN humanitarian hub in the remote northeastern town of Rann, killing three aid staff and abducting a female worker.
On Friday, ISWAP fighters in trucks fitted with machine guns raided Dikwa, sending residents fleeing.
The town, 90 kilometres (55 miles) from the Borno state capital Maiduguri, is home to more than 130,000 people, including 75,000 who had already fled from other parts of the region and were living in camps where they rely on food handouts from aid agencies.