Two explosions shook the town of Zaria in northern Nigeria's Kaduna state (today) Sunday.

At least one, of them was at a church, the emergency services and a security official told Reuters.

Islamist sect Boko Haram has often attacked church services in Nigeria, split roughly evenly between Christians and Muslims.

A report said as a result of the blast, fighting is going on in Kaduna, with heavy presence in Sabon Gari area of the town..

An account also said Christian youths have embarked on a reprisal as a result of the blast.

Boko Haram, which has become increasingly radicalised and meshed with other Islamist groups in the region, including al Qaeda's north African wing, is the leading security threat to Nigeria, Africa's top oil producer and a member of OPEC, Reuters said.

Regular attacks on Sunday church services are usually claimed by the sect, which says it is fighting to reinstate an ancient Islamic caliphate that would adhere to strict sharia (Islamic law).

Islamist militants attacked two churches in Nigeria last Sunday, spraying the congregation of one with bullets, killing at least one person, and blowing up a car in a suicide bombing at the other, wounding 41.

The Islamists' leader, Abubakar Shekau, has justified attacks on Christians as revenge for killings of Muslims in Nigeria's volatile "Middle Belt", where the largely Christian south and mostly Muslim north meet.