* Islamist sect Boko Haram has conducted such attacks in past
* But there was no immediate claim of responsibility
At least one suicide bomber drove a vehicle packed with explosives into a Catholic church in northern Nigeria on Sunday, killing and wounding several people, witnesses and police said.
Survivor Linus Lighthouse said two bombers had struck different parts of the packed St Rita's church, in Kaduna, a volatile ethnically and religiously mixed city. They had got right inside the building, causing many casualties, he said.
"I cannot tell you how many casualties, but there were many. The heavy explosion also damaged so many buildings around the area," he said.
But Aminu Lawal, a Kaduna police spokesman, said there was only one confirmed bomber and that no casualties had yet been confirmed apart from the bomber himself.
Another witness, Daniel Kazah, a member of the Catholic cadets in the church, said he had seen three bodies on the bloodied church floor. "But still others were taken to the mortuary," he said.
There was no immediate claim of responsibility but Islamist sect Boko Haram has claimed similar attacks in the past and has attacked several churches with bombs and guns since it intensified its campaign against Christians in the past year.
The Islamists are fighting to try to create an Islamic state in Nigeria, whose 160 million people are split roughly evenly between Christians and Muslims.
Some of the attacks on churches have seemed calculated to stir sectarian tensions along Nigeria's volatile middle belt, where its largely Christian south and mostly Muslim north meet.
Kaduna lies along that fault line, and many of its neighbourhoods are mixed.
A bomb in a church in Kaduna state in June triggered a week of sectarian violence that killed at least 90 people.