At least three aid workers have been killed in the northeastern Nigerian town of Rann during an attack by militants on a military facility, a United Nations spokeswoman said on Friday.
A fourth aid worker may also have been killed and another was feared abducted, the spokeswoman said. A separate UN source said the attack in Borno state was likely to have been carried out by jihadist group Boko Haram.
All the aid workers were Nigerian nationals, the spokeswoman said.
Borno state is the epicentre of the Boko Haram insurgency which aims to create an Islamic state in northeast Nigeria. More than 20,000 people have been killed and some 2 million forced to leave their homes since 2009.
A camp for displaced people in Rann was bombed in an accidental Nigerian Air Force strike last year, killing up to 170 people.