A suicide car bomber has killed at least three people at a church in the troubled central Nigerian city of Jos, sparking reprisals by Christian youths.
Witnesses said the suicide bomber drove his car into the prominent Church of Christ during morning prayers.
The radical Islamist sect Boko Haram later said that it carried out the attack.
The bombing sparked a riot by Christian youths, with reports that at least two Muslims were killed in the violence.
The two men were dragged off their bikes after being stopped at a roadblock set up by the rioters, police said.
A row of Muslim-owned shops was also burned, an AFP reporter at the scene said.
President Goodluck Jonathan condemned the violence and appealed for calm.
"Those who seek to divide us by fear and terror will not succeed," he said in a statement.
"The indiscriminate bombing of Christians and Muslims is a threat to all peace-loving Nigerians."
Earlier, the suicide bomber smashed his car through unmanned gates towards the packed church, killing a woman in the process, witnesses said.
The explosives detonated close to where members of the congregation were attending a Sunday service, killing a father and his child.
"The bomber drove at top speed, and there was a loud explosion and everything was black," said churchgoer Ezekiel Gomos.
At least 38 people had to be taken to hospital for treatment, the National Emergency Management Agency said.
The attack sparked immediate anger among Christian youths in the city.
They "were very angry and mobilised... and I overheard them saying they were going to avenge the attack," one witness said.
Ethnic and religious tensions run high in Jos, the capital of Plateau state. Hundreds of people have died in bouts of sectarian clashes over the last few years.
Boko Haram spokesman Abul Qaqa later told reporters that the group had carried out the attack.
Its aim was "to avenge the killings and dehumanisation of Muslims in Jos in the past 10 years", AFP news agency quoted him as saying.
The group has carried out a number of bloody attacks across Nigeria in its quest to overthrow the government and create an Islamic state.
Boko Haram attacked churches across the country on Christmas Day 2011, killing nearly 40 people at one church outside the capital, Abuja, alone.
It has also claimed responsibility for a string of bomb blasts around Jos on Christmas Eve 2010 that killed at least 80 people.