A policeman was killed and four people were injured in a grenade explosion in Kashmir's Sopore town Saturday, police said."Security forces were dealing with a mob of stone pelters in Sopore town early Saturday when militants lobed a grenade at a police party at around 2.30 a.m," a police officer told IANS here."Five people were injured in this explosion. One police constable who was critically injured has died," the officer added.Out of the four injured, two are critical while the remaining two suffered minor injuries.The attack occurred during the holiest Muslim night of 'Shabir-e-Qadr' when devotees across the world spend the night in prayer and penance.