Three aid workers were confirmed killed in a Boko Haram attack in northeast Nigeria, the UN said on Friday, as the government extended the search for 110 schoolgirls abducted last month to neighboring countries. The UN and two security sources initially said four people were killed in the militant attack in the remote town of Rann on Thursday evening but later revised the death toll. Rann is located some 175 kilometers east of the Borno state capital, Maiduguri, near the border with Cameroon and communications are difficult. A UN spokeswoman in Abuja, Samantha Newport, said the attack happened "after dark" outside a camp housing some 55,000 people displaced by the conflict. "Of the aid workers that were killed, two worked for the IOM (International Organization for Migration) in camp management; and one was a medical doctor working as a third party consultant for UNICEF," the UN childrens agency, she added. Three aid workers were injured and a female nurse was missing, feared abducted. All those killed, injured or missing were Nigerian. The UNs humanitarian coordinator in Nigeria, Edward Kallon, said: "Aid workers put their lives on the line every single day to provide emergency assistance to vulnerable women, children and men. "Our deepest condolences go to the families of the victims and our brave colleagues and we call on authorities to ensure the perpetrators are brought to justice and account." Mohammed Abdiker, IOM director of operations and emergencies, said the militants had "superior firepower" and were "armed with automatic weapons, rocket propelled grenades and gun trucks". "We are outraged and saddened at the killings of two of our colleagues in an attack by BokoHaram in North East Nigeria last evening," he added. Also Friday, Nigerias information ministry said the government has extended the search for 110 girls, who were taken from their school in the town of Dapchi, in the northeastern state of Yobe, by suspected Boko Haram militants on Feb. 19. Yobe state directly borders Niger and is also close to Nigerias borders with Chad and Cameroon.