At least 12 people were injured in a blast on Zoo Road in Guwahati city in Assam on Wednesday, a senior state government official said. At least one of the injured is believed to be in a critical condition.

The banned outfit United Liberation Front of Assam (Independence) claimed responsibility for the grenade explosion, All India Radio reported.

Assam Police chief Kuladhar Saikia said it is not yet clear who was responsible for the explosion. “It’s too early to conclude,” Saikia said. “We have not ruled out the possibility of the ULFA or any other militant group.”

Saikia, however, said the attack could have been triggered by “the very strong operations being carried out against the ULFA by the police with the other security forces in the last few days.”

The Army in a press statement issued in the afternoon claimed to have apprehended three ULFA cadres in upper Assam’s Tinsukia district on Tuesday.

The blast took place on a busy stretch of the road around 8 pm, East Mojo reported. A child was also wounded. The injured have been shifted to Guwahati Medical College and Hospital.

The grenade was lobbed from a moving two-wheeler, the police said. Assam Chief Minister Sarbananda Sonowal condemned the incident. Sonowal said no one will be allowed to commit such heinous actions in future. He also ordered Saikia to initiate an investigation into the incident.

Saikia said the police had beefed up security in Guwahati in the last couple of days. A high-level meeting discussing the security scenario in the state had taken place on Wednesday in the presence of the the chief minister, Saikia added.

Minister Himanta Biswa Sarma said two Sashastra Seema Bal personnel, Amulya Ratan Mahato and Ramesh Lal, were admitted to the hospital. Three others, identified as Fardeen Hasnain Rahman, Bijay Kumar Shah and Sultan Jahidur Rahman were also admitted.