Two separate attacks carried out in churches during Sunday service in Nigeria are feared to have caused the deaths of dozens.

A suicide bomber blew himself up near a church in the central city of Jos on Sunday, while gunmen attacked another church in Biu in the country's northeast, writes Al Jazeera.

A government spokesman has confirmed that a bomb carried by a suicide bomber exploded during mass in Jos, a city on the boundary between Nigeria's Muslim north and Christian south.

Earlier Sunday in Biu, a city in northeast Nigeria's Borno state, gunmen opened fire during service at a local church.

Gunmen broke into the church and opened fire on the assembled congregation, killing and wounding many, according to eyewitness reports.

No organization has assumed responsibility for the terrorist acts yet, but recent such attacks against churches in Nigeria have been carried out by Boko Haram, a militant organization fighting for imposing Sharia in the country.