UN Secretary-General, António Guterres has urged Nigerian government to step up efforts against Boko Haram.
He also called on the government to apprehend and prosecute those who carried out the attack on Rann town, in Borno.
Guterres, in a statement he signed at the weekend, also confirmed the evacuation of all humanitarian personnel and the temporary suspension of all humanitarian deliveries in the area.
He condemned the killing of three aid workers in Rann, following an attack by suspected Boko Haram insurgents.
The UN chief recalled that attacks targeting civilians and civilian infrastructure violated international humanitarian law.
“Those responsible for these and other atrocities in Nigeria must be apprehended and prosecuted,” the UN scribe said.
The Secretary-General called on all the parties to ensure at all times the protection of all civilians.
According to the UN, at least one other aid worker remains critically injured and another three are still missing while eight members of the Nigerian national security forces were also killed.
The UN chief said: “at the time of the attack, over 40 humanitarian workers were in Rann.
“All humanitarian personnel have been evacuated from Rann, and all humanitarian deliveries in the area have been temporarily suspended”.
The Secretary-General expressed his deepest condolences to the affected aid workers, their families and to the Government and people of Nigeria.
The UN scribe wished those injured a swift recovery.