A bomb exploded on a bus on Thursday in the Russian northern Caucasus region, killing five people and injuring 12 others.

According to the investigators, it could be a terrorist attack.

The incident occurred in North Caucasus where remnants of Chechen separatist groups and other militant groups fight against the government and police.

No immediate suspects were named by the authorities.

Oleg Ugnivnenko, a spokesman for the regional Emergency Situation Ministry, said that the bus was traveling from the southern city of Pyatigorsk and was near police post at the administrative border of North Ossetia when the fire started, The Associated Press reports. The blast occurred shortly thereafter.

A law enforcement official said the blast may have come from an explosive device in the road.

Still, the device is thought to have been planted on the bus when it was parked near a police post, according to a duty officer for the North Ossetia Interior Ministry.

Among the five victims there was also a child. The 12 people who got injured were treated in the hospital for burns and shrapnel wounds.

There were 19 people on the bus, including two drivers.

The region where the incident occurred, North Ossetia, is located near Chechnya, a region wracked with violence.

In 2004, in Beslan, North Ossetia, a school was the site of a hostage seizure that ended with the deaths of 330 people.

The incident from Thursday comes ahead of the parliamentary elections, due to be held in less than two weeks. The elections are a referendum on the presidency of Vladimir Putin. 

Putin used the terrorist attacks as a reason to make changes in the election laws and increase the surveillance powers of police agencies.

Law enforcement and security agencies launched warnings that terrorist attacks may be possible during the election campaign.