Unidentified men on Saturday set off a low-intensity blast in a mini bus in front of the regional headquarters of BJP in Raipur but no one was injured in the incident, police said.
"The incident occurred in front of the regional headquarters of Bharatiya Janata Party in Ekatam Parisar this evening," Raipur Superintendent of Police Amit Kumar told PTI.
Little known 'Don Group' has claimed responsibility for the blast, he said.
"We have started investigations in the incident and all angles, including the involvement of Naxals, are being probed," Kumar said.
A letter was recovered from the spot which stated that the accused were agitated over not getting proper treatment at Ambedkar Hospital, he said.
Owner of the minibus Omprakash Tiwari told PTI that the vehicle was hired by a company in Siltara village, 20 kms from Raipur, and was being used to ferry its staff.
Tiwari said the bus was parked at Ekatam Parisar at 3 pm and the blast occurred after an hour. The bus was torched later, he added.
Immediately, police, bomb disposal squad and fire brigade personnel were rushed to the spot, Kumar said.
A similar blast had occurred in front of a theatre in March last. The same group had claimed responsibility for it and had warned of more such attacks.