A bomb exploded in a Catholic church on the outskirts of the Nigerian capital Abuja during Christmas prayers on Sunday and emergency services said they did not have enough ambulances available to evacuate all the dead and the wounded.

The precise number of dead and wounded in the blast was not immediately available.

It was not known who exploded the bomb but Nigerian security forces are battling the militant Islamist Boko Haram group, which wants to impose Islamic sharia law across the country split roughly equally between Christians and Muslims.

Yes, I can confirm to you that there has been a bomb blast in a church in Madala (suburb), National Emergency Management Agency (NEMA) spokesman Yushau Shuaibu said by telephone.

We are presently there, evacuating the dead and the injured, but unfortunately we don't have enough ambulances. Most of our ambulances have gone to operate on the major highways of the country, he added.

The blast in St Theresa's Church in Madala, an Abuja suburb, blew out windows of at least one house nearby, a witness said.

There was no immediate claim of responsibility, but Islamist sect Boko Haram has been blamed for dozens of bombings and shootings in the north, and has claimed responsibility for two bombings in Abuja this year, including Nigeria's first suicide bombing on the U.N. headquarters in August that killed at least 23 people.

Last Christmas Eve, a series of bomb blasts in ethnically and religiously mixed central Nigeria killed 32 people, and others people died in attacks on two churches in the northeast of Africa's most populous nation.

BOKO HARAM BOMBINGS

Gun battles between the security forces and Boko Haram killed at least 68 people in two days of fighting in northern Nigeria, authorities and hospital sources said on Saturday.

Boko Haram has been blamed for scores of shootings and bombings in Nigeria's remote, semi-arid northeast, including a spate of attacks in the past few weeks.

Boko Haram -- which in the Hausa language spoken in northern Nigeria means Western education is sinful -- is loosely modelled on the Taliban movement in Afghanistan.

Rights groups say more than 250 people have been killed by Boko Haram since July 2010.

On August 26 a suicide bomber struck the U.N. building in Abuja. At least 23 people were killed and 76 wounded by the bombing which gutted the ground floor and smashed almost all the windows. Boko Haram claimed responsibility on August 29, demanding the release of prisoners and an end to a security crackdown aimed at preventing more bombings.

The blast was the first known suicide bombing in Nigeria. It marked an escalation in the group's tactics and revealed an increase in the sophistication of explosives it uses.

(Reporting by Felix Onuah; Writing by Tim Cocks and Peter Millership)