Kano — Christians in Nigeria's mainly Muslim north demanded Saturday that authorities do more to protect them after a woman was stabbed to death for allegedly insulting the Prophet Muhammad.Two suspects have been arrested in Thursday's killing of a middle-aged petty trader, Bridget Abihime, Nigeria's national police chief Solomon Arase said on Saturday. Abihime allegedly said the Prophet Muhammad was not important.The northern chapter of the Christian Association of Nigeria said police are not doing enough to protect Christians and warned on Saturday of a "looming religious crisis." In the past, such attacks have led to retaliation and sectarian violence."This barbarism must stop now," said the Christian association's spokesperson, the Rev John Hayab. He accused police of trying to cover up the killing and demanded all those involved in Abihime's death be arrested and prosecuted.Police chief Arase promised swift justice and called on community leaders to help in "dousing the tensions". He said all security agencies were being deployed to prevent the incident from "degenerating into a major security threat."Nigeria's 170 million people are divided almost equally between Christians mainly in the south and Muslims predominantly in thenorth. They interact peacefully for the most part. But tensions are high in the north and especially the northeast where Boko Haram's near 7-year-old Islamic insurgency has killed about 20 000 people and suicide bombings keep people in fear. Kano has suffered several such attacks.