Gunmen burst into a church in northeastern Nigeria Thursday, killing at least five and wounding 10, as a terrorist group's ultimatum ordering Christians to leave the overwhelmingly Muslim region ran out.

The attack came during an evening prayer service at a church in Gombe, a dusty state capital in Nigeria's deeply poor northeast, the church's Pastor Johnson Jauro told reporters.

"The attackers started shooting sporadically. They shot through the window of the church, and many people were killed including my wife," Pastor Jauro told Reuters in a telephone interview. "Many of my members who attended the church service were also injured."

Reports varied over whether five or six people were killed in the shootings. While no group took immediate credit for the assault, the killings bore the hallmarks of a spree of violence against Christians and pro-government Muslims staged by Boko Haram, a fundamentalist militant sect. The group, whose name means "Western Education Is Sin," killed at least 500 people last year, in near-weekly gunbattles timed with bombings of churches, mosques, banks and government building.

On Sunday, the group's purported spokesman, Abul Qaqa told journalists in a phone conference that it was issuing a three-day ultimatum for Christians to leave Nigeria's Muslim-dominated north. Former oil militants in Nigeria's largely Christian and oil-rich south have responded to the ultimatum with threats of reprisals against the region's Muslims.