Three troopers and two civilians were injured in Jammu and Kashmir's Pulwama district on Friday when militants hurled a grenade at a patrol, police said."Three CRPF troopers of 110 Battalion and two civilians were injured in a grenade explosion in Pampore town today morning," a police officer told IANS here.The grenade was lobed at a road opening party (ROP) of the Central Reserve Police Force (CRPF) in the town on the Srinagar-Jammu national highway, he said.ROPs are advance patrol groups of the security forces meant to secure major highways and VIP routes in the state from landmine explosions and guerrillas attacks.In addition to hi-tech bomb detection equipment and tracers, the ROPs also employ sniffer dogs to sniff out suspected explosives planted by guerrillas.Police said the injured were shifted to hospital and the area has been surrounded for searches.Traffic was halted and markets spontaneously shut in the otherwise busy saffron-rich Pampore town after the explosion.The town in situated 14 km away from Srinagar city on the strategic Srinagar-Jammu national highway.