Nigeria's authorities are investigating the killings of at least 26 people in an attack on a college hostel in the north-eastern town of Mubi.Most victims were students called out by name by the gunmen, police said. A resident said the attackers went from door-to-door, shooting or stabbing.It is unclear who is responsible.Monday night's attack came days after dozens of people with suspected links to the Boko Haram militant group were arrested in the town.However, officials have not ruled out a recent student union election dispute as being the trigger for the violence at Federal Polytechnic Mubi.If that proves to be the case it will shock many Nigerians, as violence amongst students has never reached this level before, the BBC's Will Ross in Lagos reports.A curfew has been in force between 15:00 (14:00 GMT) on Tuesday and 06:00 (05:00 GMT).The college has been closed and some students have fled the town. Bodies in linesPolice in Adamawa state said the gunmen had inside knowledge, but stressed that the motive for the attack was not yet clear.Accounts of the attack vary - one local resident said at least 40 people had been shot dead or stabbed.A recent attack by Boko Haram militants on mobile phone masts in the area makes it hard to get information from the town.Reports suggest men in military uniform entered a hall of residence outside the main campus shortly before midnight and gathered the students outside their rooms.Some were shot dead and others stabbed with knives, and their bodies left in lines outside the buildings.Some of the dead in Mubi were Muslim while others were Christian. Two security guards and an elderly resident were among the victims, the police said.Residents are now only free to move around for a few hours each day because of a curfew imposed by the authorities.Boko Haram has not yet commented on the attack. It is fighting to establish Islamic law in Nigeria and has killed more than 1,000 people in numerous attacks across northern and central areas this year.Adamawa state has a mixed Muslim and Christian population and borders Borno state, where Boko Haram came to prominence in 2009, staging an uprising in the capital Maiduguri.