One witness at the church in Biu, Hamidu Wakawa, said that "gunmen came to the premises of the church and started firing at people outside the church before going into the main building to carry on their killings", Reuters reported.

Officials said one woman had been killed and at least three wounded.

In a country already divided along religious lines these attacks have the potential to trigger further clashes between Muslims and Christians.

The government set up a panel to make a report and recommended that the government make compensation. People were killed and businesses set on fire. But no compensation has been made yet.

There is also the new aspect of Boko Haram. The bombing has been intensified. It spread from Maidugiri to Potiskum to Bauchi to Gombe to Jos and later to Kano. It became a very worrisome situation.

Later on Sunday, gunmen opened fire on another church in the north-eastern city of Maiduguri. Five people, including a pastor, were killed in the attack at the Church of Christ in Nigeria (COCIN) building.

War on Christians

Nobody has yet claimed responsibility for Sunday's church attacks, but most people suspect militant Islamist group Boko Haram, which in March declared "war" on Christians.

Of two million Iraqi refugees currently outside of the country, some 30 per cent are minorities, mostly Christians, according to the UN: the bulk of them in Syria, Jordan and Turkey, unable to work and living in desperate poverty. Many in Syria now fear that it will become another Iraq, with Christians caught in the crossfire between rival Islamic communities.