A large explosion has struck a church on the outskirts of Nigeria's capital, causing an unknown number of casualties.

Witnesses say the explosion happened Sunday during Christmas services in the St. Theresa Church, located in Madalla, a suburb of Abuja.

There was no immediate claim of responsibility.

A spokesman for the National Emergency Management Agency confirmed there are casualties but could not give a precise figure. He also said the agency did not immediately have enough ambulances to transport all the wounded.

Nigeria has endured a wave of deadly violence in recent months, much of it blamed on the radical Muslim sect Boko Haram.

Authorities say at least 68 people have been killed over the past few days in the country's north, in clashes between Boko Haram and government security forces.

Nigeria has also witnessed periodic bouts of sectarian fighting over the years, much of it between Muslims and Christians in the central city of Jos.