At least 70 people have been killed in the past three days in Nigeria after church bombings sparked violence in two northern Nigerian cities.

Suicide bomb attacks on churches in Kaduna and Zaria Sunday left more than 20 people dead and sparked reprisals by Christian mobs. Officials say 52 people were killed and more than 100 others were injured in the violence in Kaduna state.

On Monday, violence also broke out in the city of Damaturu where more than 20 people have ben reported killed since Monday. Witnesses say that members of the Islamist militant group Boko Haram started gunfire attacks in several places. Police told VOA Tuesday that at least three security officers were also killed.

Officials in Kaduna say protesters took to the streets Tuesday, setting buildings on fire and burning tires. Kaduna state commissioner of information Saidu Adamu told VOA that authorities are blaming both Christians and Muslims for the unrest in the religiously mixed city.

“We can not pinpoint one particular religion to say they are responsible now. Every group is responsible. We are not trying to pinpoint. All we are trying to do now is to make sure the crisis is brought to an end.”

The unrest has prompted officials in both Damaturu and Kaduna to impose 24-hour curfews.

Violence in the north has escalated in recent weeks, prompting fears of a wider sectarian conflict. Boko Haram claimed responsibility for Sunday's attacks on three churches as well as church attacks the previous two weeks.

The violence has continued despite increased security by Nigeria's anti-terrorist Joint Task Force.

Nigeria has a history of sectarian violence, especially in the country's Middle Belt, where the mainly Muslim north meets the predominantly Christian south.

Boko Haram says it is fighting for an Islamic state and does not recognize the Nigerian government or the constitution.