Police said the grenade missed the target and exploded on the road, injuring four civilians who had to be taken to hospital.

'One of the injured persons is in critical condition,' said one of the doctors treating the victims.

Islamist militants have picked up their activities in the Kashmir valley after street protests called by separatists subsided with the arrest four policemen who have been charged with the rape and murder of two women in south Kashmir Shopian district on May 30.