After an initial lull in violence following the announcement of a state of emergency in three northern Nigerian states, violence has been increasing over the past few months, Open Doors USA reports. The Islamic extremist group Boko Haram attacked a secondary school dormitory in Yobe around 1 a.m. on Sunday, killing more than 40 students. Although initial reports indicated that mostly Muslim students had died, Open Doors has learned that there may be some Christian students among them. The attack came just after the government, promising protection, had urged schools in Yobe to re-open after earlier similar attacks. Earlier this month, presumed Boko Haram fighters in Borno, Yobe and Maiduguri set up checkpoints and fired at motorists and bystanders. At least 10 Christians have died in these attacks, including a youth leader of an ECWA church in Maiduguri and a medical student. Open Doors has also received word that a pastor and his son were killed on Thursday night in Yobe when their church was burned to the ground. One eyewitness of Sunday's attack in Yobe told Reuters, "They started gathering students into groups outside, and then they opened fire and killed one group and then moved onto the next group and killed them. It was so terrible." President Goodluck Jonathan called the attack "the creation of the devil." It came just a few days after the school re-opened following widespread closures after militants attacked Mamudo School outside Damaturu and killed 29 pupils and a teacher on July 6. Two weeks ago, the state commissioner for education, Mohammmed Lamin, urged all schools to re-open and promised protection from soldiers and police. "The renewed violence is creating uncertainty and fear among people," reported an Open Doors worker. "It is intensifying an already explosive atmosphere as the government continues its battle against Boko Haram." Nigeria is ranked No. 13 on the Open Doors 2013 World Watch List of the worst persecutors of Christians.