March 2 (UPI) -- Boko Haram militants attacked a military base in Nigeria's northeastern Borno State, killing three U.N. aid workers and leaving another missing, U.N. officials said Friday.
A statement from the International Organization for Migration, a U.N. agency, said militants armed with automatic weapons, rocket-propelled grenades and gun trucks attacked the base in Rann on Thursday.
Three U.N. workers -- two from the IOM and one from UNICEF -- died, as well as four soldiers and four mobile police. Three other humanitarian workers were injured and one, a nurse, was missing.
"We strongly condemn this attack on selfless aid professionals, who were working in the most difficult humanitarian conditions," said Marie-Pierre Poirier, UNICEF regional director for west and central Africa.
"Alarmingly, the number of attacks on aid workers is increasing around the world, and we must stand together to reaffirm our commitment to protect them. Humanitarian workers should never be a target," she added.
The IOM said about 55,000 displaced people were living in a camp near the base at the time of the attack.
In January 2017, the camp was the site of two attacks, a mistaken government bombing and a Boko Haram attack.