Militants lobbed a grenade on a police vehicle carrying an undertrial at busy Batamaloo bus stand around noon, police said.
The grenade landed and exploded inside the vehicle, resulting in injuries to four policemen, the undertrial Shakeel Ahmad Khatana and a civilian, Ghulam Nabi, who was passing through the area, was also injured , police said.
Khatana, whose condition is stated to be critical, was being shifted to Baramulla district jail from Panthachowk police station.
This is the first militant strike in Srinagar since the Muslim fasting month of Ramzan began last week.
(with agency inputs)