Authorities in Nigeria said 11 people were killed and 18 others critically wounded in an attack on a church in the southeastern part of the country.

Initially witnesses said the attack was carried out by at least two gunmen, but Garba Umar, police commissioner of Anambra state, said one gunman attacked St. Philip Catholic Church early Sunday.

Anambra State Governor Willie Obiano said the attack stemmed from a feud between members of the local community who were living outside Nigeria.

"We are not going to relent until we bring those that perpetrated this heinous crime to book," he said.

Nigeria's southeast is predominantly Christian and the attack is a rare act of violence at a church.

No group has claimed responsibility for the attack, but police said they do not believe Boko Haram militants were behind it.

Nigeria is wracked by insecurity. The Islamist insurgency Boko Haram has killed more than 20,000 people since 2009, sparking one of the world's largest humanitarian crises.

