The grenade, however, exploded outside injuring two policemen and four civilians, a police officer said.
"The alert SPO threw out the grenade to safer place and saved lives of dozen police, CRPF and civilians in Sopore," a police spokesman said.
According to police, terrorists threw the grenade at a security forces vehicle in the main market near the State Bank of India branch and it entered the vehicle.
"We have registered a case, investigation is underway," SSP Harmeet Singh said.
The injured were taken to a nearby hospital where their condition is said to be stable, a police officer said.
Soon after the grenade attack, police and paramilitary forces launched a search operation to nab the militants responsible for the grenade attack.
Meanwhile, a terrorist was shot dead in the morning during an encounter with security forces in Jammu and Kashmir's Uri sector. A heavy gunfight started after the Army saw a group of terrorists moving in the forest at Kalgai village near the Line of Control. Two to three terrorists are suspected to be trapped there, Army sources said.
(With inputs from IANS)