SRINAGAR: Helicopters and drones circled the air and more than 4,000 troops today fanned out across south Kashmir 's Shopian district in a massive operation to flush out militants holed up inside homes.The operation targeting militants who have been hiding in the area and striking against security forces began in the early hours of the morning with security forces, comprising army, police and CRPF, marching into more than a dozen villages in the district, army sources said.There have been no casualties so far.The operation in Shopian, about 55 km from here, was perhaps the biggest in more than a decade in the troubled Kashmir Valley, an army official said on the condition of anonymity.Door-to-door search of houses, a practice stopped in the late 1990s, was re-introduced today. The troops asked all villagers to assemble in a common area so a proper search of their homes could be carried out,"We do not wish to have any civilian casualty and the measure was therefore required," said a senior army official engaged in the operation.The cordon and search operation (CASO) followed intelligence inputs about the presence of militants, including foreign terrorists , in the area, an official said. However, no contact had been established with the militants so far.Aiding the security forces, which included a team of concealed anti terrorists (CAT), on the ground were drones providing real-time intelligence to the troops.Barring a minor stone pelting incident at Turkawangan village, the operation was going on smoothly, an official said.After carrying out a search operation, security forces carried out a 'reverse sweep' of the entire region once again in order to ensure that none of the militants had slipped in after the earlier cordon ended.In Delhi, Army Chief Gen Bipin Rawat, who was here on a two-day visit earlier this week, indicated to reporters that security forces had beefed up counter-infiltration postures in Jammu and Kashmir."It is nothing new. Combing operations have been going in the past as well," he said.He said there had been an increase in militant activities in south Kashmir with incidents of policemen being killed and banks being looted.The operation comes four days after militants killed seven people, including five policemen, in adjoining Kulgam.Recently, videos of large groups of militants -- in some cases as many as 30 -- have surfaced on social media, despite the ban imposed by authorities on 22 such sites and applications.Security agencies believe that these videos were shot in south Kashmir, especially Shopian district.