CNN

(CNN) -- A northeastern Nigerian state was under a 24-hour curfew Saturday following three days of violence that left more than 30 Christians dead.

The curfew was placed in effect as fears rose that Christian youths could launch reprisal attacks, said Tomborokai Gajere, chaplain to the Adamawa state government.

On Friday, 11 men and one woman were killed in the city of Yola.

The militant Islamist group Boko Haram has claimed or been blamed for a recent spate of sectarian attacks.

On Thursday, it was reported that 17 people, all Christians, were killed while mourning the deaths of two others who were killed the day before. These attacks happened in the city of Mubi. Daniels said the official number of deaths was just 12, with four injuries.

Gajere said he personally pleaded with Christian youths in Numan, which is near Mubi, for calm amid reports that reprisal attacks were possible.

Nigerian President Goodluck Jonathan condemned the recent attacks in a speech to the nation Saturday, saying such "mindless acts of violence ... are unfortunate."

"I urge all Nigerians to eschew bitterness and acrimony and live together in harmony and peace. Wherever there is any threat to public peace, our security agencies will enforce the law, without fear or favor," Jonathan said.

Boko Haram has been blamed for months of widespread bloodshed in Nigeria, with churches and police stations among the targets.

The group also claimed responsibility for a series of attacks on churches on Christmas Day.

The latest sectarian attack comes as Nigeria also faces a nationwide wave of popular protests over the removal of a gas subsidy that had kept prices artificially low. Police have responded forcefully by making many arrests, an effort that has contributed to at least one death.

Jonathan's speech Saturday defended the decision to remove the subsidy.

"My fellow Nigerians, the truth is that we are all faced with two basic choices with regard to the management of the downstream petroleum sector: Either we deregulate and survive economically, or we continue with a subsidy regime that will continue to undermine our economy and potential for growth and face serious consequences," he said.

He acknowledged that deregulating the oil sector is "not a magic formula," though he said "it provides a good entry point for transforming the economy, and for ensuring transparency and competitiveness in the oil industry, which is the mainstay of our economy."

Jonathan added that a committee will be established to oversee the removal of the gas subsidy "to ensure that the funds ... are spent prudently on projects that will build a greater Nigeria."

Journalist Hassan John contributed to this story for CNN.