Six persons were injured in a powerful hand grenade explosion at Sopore, 54 km north of Srinagar in Baramulla district.
Police said the militants tossed a hand grenade at security personnel at the main bus stand in Sopore, which exploded after missing the target, injuring civilian bystanders.
The injured were taken to a hospital in Sopore, where attending doctors referred four critically injured to Srinagar for specialised treatment.
No group has claimed responsibility for the attack.