MAIDUGURI, Nigeria - Fighting between a radical Muslim sect and paramilitary forces in Nigeria has killed at least 61 people over several days of violence in the nation's northeast that has left churches bombed and people hiding in fear, authorities said.

In hard-hit Yobe state, where at least 50 people died, the government on Saturday ordered a dusk-till-dawn curfew following attacks by the sect known as Boko Haram. In Maiduguri, the capital of neighbouring Borno state, bombs reduced at least three churches to rubble and raised fears of further attacks by a group that claimed Christmas Eve bombings last year that killed dozens.

The fighting began Thursday in the two states, with gunfire and explosions heard into the night and the following day in an arid region that borders Cameroon, Chad and Niger. Damaturu, the capital of Yobe state, and the town of Potiskum bore the brunt of the violence.

In Damaturu, residents fled their homes near the city's central mosque ahead of a combined attack by soldiers and the federal police's feared Mobile Police, known as "kill-and-go" for their propensity for violence. The paramilitary forces raided the area in armoured personnel carriers and tanks, with heavy gunfire marking their arrival.

"We were able to kill 12 of the Boko Haram armed sect and bombers," local police commissioner Lawan Tanko said. The police commissioner said officers also recovered Kalashnikov rifles, ammunition and explosives.

In Maiduguri, the capital of Borno state, a mortuary official who requested anonymity because of the sensitivity of the matter told The Associated Press at least 11 bodies had been brought in from the violence. Authorities blamed Boko Haram for firebombing at least three churches around the capital, attacks that killed one pastor and his young child.

This is just the latest in a series of bombings over the last year by Boko Haram. The group, whose name means "Western education is sacrilege" in the local Hausa language, wants to implement strict Shariah law across a nation of more than 160 million people that is home to both Christians and Muslims.

Boko Haram claimed responsibility for a Nov. 4 attack on Damaturu, Yobe state's capital, that killed more than 100 people. The group also claimed the Aug. 24 suicide car bombing of the U.N. headquarters in Nigeria's capital that killed 24 people and wounded 116 others.

While initially targeting enemies via hit-and-run assassinations from the back of motorbikes, violence by Boko Haram now has a new sophistication and apparent planning that includes high-profile attacks with greater casualties. The sect is responsible for at least 465 killings in Nigeria this year alone, according to an AP count.

Boko Haram has splintered into three factions, with one wing increasingly willing to kill as it maintains contact with terror groups in North Africa and Somalia, diplomats and security sources say. That, as well as its increasingly violent attacks, have some worried the group will carry out further attacks around Christmas and New Year's.

Last year, a series of Christmas Eve bombings in the central Nigerian city of Jos claimed by Boko Haram killed at least 32 people and wounded at least 74 others.

With those attacks in mind, the U.S. Embassy in Nigeria's capital of Abuja issued a warning Friday to citizens to be "particularly vigilant" around churches, large crowds and areas where foreigners congregate.

Analysts say the government's response remains strained as President Goodluck Jonathan, a Christian from the country's south, remains worried about alienating the country's predominantly Muslim north with heavy-handed tactics. In 2009, a military and police crackdown following rioting by Boko Haram members in and around Maiduguri left 700 people dead.

Yet since Thursday, authorities have been using paramilitary police and soldiers more freely. Tanko, the Yobe state police commissioner, said joint patrols by the military and police would continue.

"When you are fighting people you don't know, you cannot say that's the end of the exercise," Tanko said. "We are trying to ensure that will be the end, but we are monitoring what is going on. But we know we cannot specifically say that will be the end."