MAIDUGURI, Nigeria (AP) — Police yesterday blamed a radical Islamist sect for attacks that witnesses say left 18 people dead over the past two days in Nigeria's troubled north, part of a cycle of spiraling violence that is exacerbating religious tensions and that the government has been powerless to stop.

Meanwhile, members of a largely Muslim community in the small village about 30 miles from Nigeria's largest northern city of Kano turned against its Christian minority after a trader was accused of insulting the Prophet Muhammad, police said yesterday. Although police say nobody died in the violence, a witness reported seeing four dead bodies.

Christians and Muslims have lived together peacefully across the country of 160 million for years, but the growing violence is creating a climate of religious distrust and local communities have lost faith in the government's ability to protect them.

Suspected members of the radical lslamist sect known as Boko Haram carried out three attacks Wednesday and Thursday in different parts of the northeastern city of Maiduguri, said Borno state police spokesman Gideon Jibrin. Jibrin declined to say how many people had been killed overall, but witnesses said 18 people died — including three children.

Boko Haram did not immediately claim responsibility. The group is believed to be responsible for more than 740 deaths this year alone, according to an AP count, and is also blamed for attacks targeting mosques, churches, schools, phone masts and government buildings.

Separately, Kano state police chief Ibrahim Idris said Thursday nobody died in the religious violence in a town in the state, but resident Sadiq Ahmed said he saw four dead bodies outside Christian-owned shops that had been set ablaze. Ahmed also said he saw a burned-down church.

Idris said he believes the trader was misunderstood and that the situation is now calm.

Earlier this week, a Christian vigilante group in central Nigeria killed a Muslim resident after he defied an illegal checkpoint the group had put up to protect their church from a Boko Haram attack, even though the sect had not previously struck in that area. The killing sparked riots that left 10 people dead.

President Goodluck Jonathan, whose government has responded to the crisis by sending more troops to the most affected areas, recently said on state-run television that Boko Haram remained a "faceless" group and that there was nobody for the government to meet with to seek peace.