Witnesses say bombers and gunmen attacked two churches in Nigeria on Sunday, one in the northeastern region and the other in central Nigeria.

There are reports of casualties at both sites, but it was not immediately clear how many people were killed or wounded.

Witnesses say a bomb detonated outside a Christian church in city of Jos. It is located in Nigeria's so-called “middle belt” region, which divides the mostly Muslim north and predominantly Christian south.

The second attack took place at a church in the city of Biu in northeastern Borno state. There are conflicting reports about whether the Biu attack was carried out using bombs or guns or both.

There was no immediate claim of responsibility for the attacks.

The radical Islamic group Boko Haram claimed responsibility for a similar attack on June 3rd. A suicide bomber killed at least 15 people during a church service in the capital of northeastern Bauchi state.

Boko Haram is blamed for hundreds of killings in Nigeria, mostly in the north, since 2009.

The group does not recognize Nigeria's government or constitution and says it is fighting to establish a strict Islamic state.

Nigeria is Africa's most populous nations with a population of about 150 million people, divided roughly between Muslims and Christians.