Three soldiers and a civilian were injured on Thursday when militants ambushed their vehicle in Jammu and Kashmir's Shopian district, officials said."Exchange of fire occurred between a returning column in Imam Sahib area. The operation against terrorists is under way," Army spokesperson Col. Rajesh Kalia said.Police confirmed the number of those injured.Reports from the area said the civilian who was driving the vehicle sustained critical injuries.The security forces had carried out a massive search operation in 20 villages of the district to trace militants responsible for recent attacks on policemen, political activists and also those involved in the recent spate of bank robberies.