At least 24 people were injured on Tuesday when suspected NDFB insurgents hurled a grenade at a computer shop in Uttarborbeel market at Howraghat in Karbi Anglong district.
Police said, the injured were taken to nearby Nagaon civil hospital where the condition of seven was stated to be critical.
Initial reports had suggested it was a bomb blast, they said, adding that police have rushed to the remote area in Howraghat police station.