However, no one was injured in the blast as the incident took place at around 6 AM.
Quoting jail guards, the police said three miscreants covering their faces came in a blue colour motorcycle and escaped immediately after hurling the bombs.
"We have registered a case in this connection and investigating the matter," said an officer of the Choudwar police station.
A similar incident had taken place here late last year apparently at the behest of an under-trial prisoner, who had been demanding free movement and better facilities inside the jail.