Nigeria has been hit by a fresh wave of violence apparently targeting the country's Christian communities. At least 17 people were killed in Mubi in Adamawa state as gunmen opened fire in a town hall where members of the Christian Igbo group were meeting. There were also reports of a deadly attack in Adamawa's capital, Yola. The Islamist Boko Haram group said it had carried out the attack in Mubi and another in Gombe on Thursday night in which at least six people died. The group has staged numerous attacks in northern and central areas in recent months - on Christmas Day it attacked a church near the capital, Abuja, killing dozens of people. One Boko Haram faction has warned all southerners - who are mostly Christian and animist - to leave the mainly Muslim north of Nigeria. Adamawa state borders Borno state, where Boko Haram emerged. Last week President Goodluck Jonathan declared a state of emergency in Yobe and Borno states, as well as Plateau state in central Nigeria and Niger state in the west, following a surge in ethnic and sectarian violence. But the pace of attacks has increased and he must now consider whether to extend the state of emergency into other states and beef up the military presence in the north in response, says the BBC's Mark Lobel in Lagos. Meanwhile, the government is also facing the bleak prospect of a general strike in two days' time amid popular fury over its removal of a fuel subsidy which has seen fuel prices double for ordinary Nigerians. 'Planning to flee'< Residents told the BBC that those killed in Mubi belonged to the Igbo community from the south of the country. They had been meeting to organise how to transport the body of an Igbo man who was shot dead by gunmen on motorbikes on Thursday evening. "It was while they were holding the meeting that gunmen came and opened fire on them," a resident said. Witnesses said gunmen burst into the hall and shouted "God is great" as they opened fire. Members of the Igbo community in northern Nigeria often own shops and businesses, but the BBC's Abdullahi Tasiu in Yola says many Igbo traders in Mubi town are reported to have closed their shops and be planning to flee the area. 'Extending out frontiers' Later, a man claiming to be a spokesman for Boko Haram told local media the group had carried out both the Mubi and Gombe attacks. "We are extending our frontiers to other places to show that the declaration of a state of emergency by the Nigerian government will not deter us. We can really go to wherever we want to go," said Abul Qaqa. He said the attacks were "part of our response to the ultimatum we gave to southerners to leave the north" and called on the government to release all Boko Haram prisoners. Later on Friday, there were reports that eight people had been killed in another attack on a church in Yola. "Some gunmen went into the church and opened fire on worshippers killing some people and wounding several others," a local journalist told the AFP news agency. A source at the local hospital told AFP that between eight and 10 bodies had been taken there. Police have also been engaged in a gun battle with suspected members of Boko Haram in another north-eastern city, Potiskum, in Yobe state. "Gunmen who are, from all indications, members of Boko Haram came in large numbers and have encircled police headquarters. They chanted 'Allahu Akbar' [God is Great] and fired indiscriminately," a resident told AFP. Boko Haram, whose name means 'Western education is forbidden', is fighting to overthrow the government and create an Islamic state More than 500 people have been killed by the group over the past year. On Christmas Day, it carried out a string of church bombings which killed 37 people at one church outside the capital, Abuja, alone. President Jonathan, who is a Christian, has vowed to crack down on the group but Christian groups have accused him of not doing enough to protect them.