Churches in northern Nigeria were targeted in three separate bombings. At least 21 people were killed and scores were wounded in the attacks, which have sparked reprisals.

"From where I stood I could see a badly destroyed church still burning from the explosion. It is obvious there were deaths from the scale of the damage and the fire," resident Mahmud Hamza told news agency AFP.

Officials said the first two attacks occurred within an hour of one another on Sunday in the Nigerian city of Zaria.

A third blast hit a church in the city of Kaduna, the number of casualties from the attack remains unclear.

The attacks have been met with reprisals by Christian youths, who have dragged Muslims from cars and killed them, witnesses said.

Christians increasingly targeted

No one has claimed responsibility for the blasts, but the Islamist group Boko Haram claimed it was responsible for similar attacks just one week ago.

Boko Haram aims to reinstate an Islamic caliphate in the mostly Muslim northern Nigeria and has been increasingly targeting Christians in recent months.

At Easter, for example, a blast killed 38 people in Kaduna. And a Christmas suicide bombing of a Catholic church in Madalla killed 44.

Some experts believe the anti-Christian attacks are being used to try and spark sectarian unrest in the nation.

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

Police and the military cordoned off the areas around the churches, and authorities have reportedly imposed a 24-hour curfew following the attacks.

tm/jlw (AP, AFP, Reuters)