Motorcycle borne youths lobbed a grenade near Bolanguri bus stand at Kuklun Road area of Bijni town critically injuring three persons working in a garage nearby.
In another incident within a few minutes of the first, another grenade exploded near No 2 Bhetgaon area of the town but nobody was injured in the explosion.
The injured, identified as Palan Mandal, Sujannam Das and Sujan Arya, have been hospitalised in a critical condition.
A massive search operation has been launched to nab the culprits.