An explosion struck a church in Nigeria's capital, Abuja, during a Christmas service Sunday, killing at least 15 people.

Another blast was later reported near a church in the central Nigerian city of Jos. It was not immediately clear if that blast targeted the church or caused any casualties.

The explosion in Abuja happened during Christmas Mass in the St. Theresa Church, located in the suburb of Madalla. Rescue officials report collecting 15 bodies, though they warned the final death toll could be higher.

Witnesses say there was tension after the blast, with angry youths setting up burning barricades, and police trying to disperse them by firing into the air.

It remains unclear what caused the blast, and there has been no claim of responsibility.

The West African country has struggled with a wave of violence centered in the country's north, where security forces are battling the radical Muslim sect Boko Haram.

Authorities say violence in and around the cities of Maiduguri and Damaturu has killed at least 68 people over the past few days.

Hundreds of others have died this year in bombings and shootings blamed on Boko Haram.

In Jos, thousands of people have died in recurring bouts of Muslim-Christian violence over the past decade. The city sits in Nigeria's Middle Belt, where the mostly Muslim north meets the mainly Christian south.

The country of 150 million is about evenly divided between the two religions.