At least 20 people have been killed by a series of bombings targeting buses in a predominantly Christian neighborhood in Nigeria's northern city of Kano, International Christian Concern reports. The official death toll is expected to rise as security officials continue to examine the scene of Monday's attack. Officials suspect the series of explosions were likely initiated by suicide bombers, though investigators are still collecting evidence to confirm that theory. Because the attacks took place in a Christian area of Kano, most officials suspect Christians were the target of the attack. The Islamic extremist group Boko Haram is suspected to be behind the bombings, but the group has yet to take responsibility. Since 2009, Boko Haram has been engaged in an armed insurgency in Nigeria's northern states, attempting to carve out a separate Islamic state where it can institute sharia law. As part of its bloody campaign to drive all Christians out of Nigeria's northern states, Boko Haram has targeted the Christian minority there by perpetrating suicide bombings at churches and killing Christians in their homes.