ABUJA, Nigeria (AP) — Four security officials were killed in a car bomb targeting a former government official in southeast Nigeria, authorities said Tuesday.

Three police officers and a paramilitary official were killed in the attack in Imo State on a convoy carrying the former governor Ikedi Ohakim, Police Commissioner Mohammed Barde said.

“The man (Ohakim) was ambushed and he was able to maneuver and escape," said Barde. The four security personnel were killed in a different car, he said. The attack was an unfortunate setback to government efforts to restore peace in some of Nigeria’s conflict-ridden southeastern states, said Barde.

Southeast Nigeria has experienced a rise in violent attacks in recent years, often blamed on separatists trying to break away from the West African nation to form an independent country. The separatists who identify themselves as the Indigenous People of Biafra have become more violent amid calls for a referendum. Their attacks often target prominent people and security forces in the southeast, say conflict experts.

A manhunt to arrest the assailants has begun, said authorities.

The attack has raised fears among local residents who are concerned that security will be threatened in the area during the country's presidential elections in February.

The violence comes months after an ambush on a lawmaker in the southeastern Anambra State which killed four police officers in September. After that incident last year, Nigerian President Muhammadu Buhari said he is “deeply concerned” about the troubled region.