(CNN) -- Under the cover of darkness, gunmen approached a college dormitory in a rural Nigerian town and opened fire on students who were sleeping.
At least 21 died, according to Nigerian President Goodluck Jonathan.
The gunmen fired indiscriminately on the male dorm, said Lazarus Eli, a military spokesman. The attack took place at about 1 a.m. Sunday at the College of Agriculture Gujba.
"So far all evidence points to the Boko Haram," Eli told CNN by phone.
There was no immediate claim of responsibility.
Part of a pattern?
Since 2009, Boko Haram has sown murder and mayhem in Nigeria's northeastern region. The Islamic militant group's name translates from the local Hausa language as "Western education is a sin."
Boko Haram militants often target schools and churches. In 2011 and 2012, Christmas attacks were blamed on them.
Jonathan created a new wing of the military to specifically deal with the insurgency.
In May, Jonathan declared a state of emergency in three northeastern states. He cited "terrorists" who have caused a "a near breakdown of law and order."
One of the three states is Yobe, where Sunday's attack took place.
It was the third attack on a school in four months in Yobe.
The ongoing violence in this predominantly Muslim region has claimed thousands of lives.
Meanwhile, human rights groups have accused the military of committing atrocities against civilians.
During a May trip to the country, U.S. Secretary of State John Kerry said Nigeria "has acknowledged that there have been some problems" and was "working to try to control it."