The Islamic extremist group Boko Haram is claiming responsibility for recent coordinated attacks against Christian villages in Nigeria's Plateau State, CBN News reports. Last Saturday, hundreds of assailants armed with guns and machetes stormed a dozen Christian villages in the city of Jos, killing 58 people. "We thank [Allah] for our success in the attack on Christians at Barikin Ladi and Riyom, whereby security agents, Christians and two state and national assembly members were killed," Boko Haram said in a letter signed by its leader, Abul Qaqa, on Tuesday. "We are also informing Christians all over the country to embrace Islam or they will be attacked. If they fail to do so, there is nobody to blame but themselves." At a June congressional hearing, Ayo Oritsejafor, the president of the Christian Association of Nigeria, urged U.S. lawmakers to officially declare Boko Haram a terrorist organization. To date, the U.S. State Department has only designated three Boko Haram leaders as terrorists. "By refusing to designate Boko Haram as a foreign terrorist organization, the United States is sending a very clear message not just to the federal government of Nigeria but to the world that the murder of innocent Christians and Muslims who reject Islamism -- and I make a clear distinction here between Islamism and Islam -- are accepted losses," Oritsejafor said.