Lagos, Nigeria (CNN) -- Nigeria's Christians are losing faith that the government will protect them from attacks by Islamic extremists and will "respond appropriately" to future killings, the country's leading church group warned Wednesday. In a public message to President Goodluck Jonathan, the Christian Association of Nigeria called the Christmas Day targeting of churches in several cities "a declaration of war on Christians and Nigeria as an entity." The group also criticized its Muslim counterparts for failing to condemn the Islamic militants blamed for Sunday's attacks, calling their responses "unacceptable." "The Christian community is fast losing confidence in government's ability to protect our rights to religious liberties and life," its president, Pentecostal pastor Ayo Oritsejafor, said in the statement. "The consensus is that the Christian community nationwide would be left with no other option than to respond appropriately if there are any further attacks on our members, churches and properties." Nigerian official condemns attacks Jonathan responded with a statement of condolences for the attacks, which the church group said killed more than 50 worshippers, and a call for Nigerians to unite behind the government's efforts to pursue those responsible. Nigerian authorities have blamed Boko Haram, a fundamentalist Islamic movement that mounted similar attacks the previous Christmas. "The best thing is for all religious leaders, opinion and traditional leaders, youth leaders and women leaders to come together and assist government," Jonathan said. He pledged that his administration "will surely do more," but added, "The terrorists are human beings. They are not spirits." "They live with us. They dine with us," he said. "We know them. People know them. As long as Nigerians are committed to expose them, we will get over this ugly situation." Nigeria's 150 million people are divided almost evenly between predominantly southern Christians and northern Muslims. Clashes between the two groups have flared periodically for years, but Boko Haram -- which wants to establish a state based on Islamic law in the north -- has stepped up the violence with a series of high-profile attacks in the past two years. The group claimed responsibility for an August car bombing at the building that houses U.N. offices in Abuja, which killed 25 people, and an assault on the town of Damaturu in November that left more than 100 dead. The church group criticized Islamic leaders in the north for what it called their inaction in the face of the attacks, calling it "unacceptable and an abdication of their responsibilities over their extremist members." "It is on record that most religious, traditional and political leaders in the North have not come out openly to condemn the extremist activities of Boko Haram," the group said. "We hold them responsible for what is happening, because they have not taken concrete steps to check the excesses of their members." There was no immediate response to the statement from Muslim groups. But Jonathan called on leaders of both faiths "to work together, because terrorism is like a cancer to the body -- it starts from somewhere and spread to all the organs of the body." Jonathan has led Nigeria since 2010, becoming acting president that May and winning a full term in April. He has deployed government troops across northern Nigeria in an effort to destroy Boko Haram, a step he told the Christian leaders was overdue. "At the beginning, if the appropriate response was given then over this, they couldn't have developed to this level," he said.