Explosion kills 5 near bus station

• The blast occurred in Azare town in Bauchi state


• Police: It's too early to tell whether Boko Haram militants are behind it

Abuja, Nigeria (CNN) -- An explosion near a bus station left five people dead and 12 others injured in northern Nigeria, police said Thursday morning.

The blast occurred in Azare town in Bauchi state on Wednesday night.

A man left a bag filled with explosives outside a bus station in the town, which went off, witnesses said.

"We are investigating the matter and we'll get the culprits behind it," said Mohammed Haruna, a spokesman for the state police."It's premature to comment on whether Boko Haram are behind the attack."

Azare is the second-largest town in the state. Boko Haram militants have attacked the town several times, especially in 2011 and 2012.

The militant group, which aims to institute Sharia law, has targeted northern areas including Yobe, Kano, Bauchi, Borno and Kaduna.

Aminu Abubakr contributed from Bauchi and Lillian Leposo from Abuja