Srinagar: An officer of the Indian Army and three security personnel, including a constable of the Border Security Force or BSF, were killed in the line of duty during a major anti-terror operation along the Line of Control or LoC in Jammu and Kashmir's Kupwara district, officials said.

Three terrorists were also gunned down in the anti-terror operation, which took place in north Kashmir's Machil sector, they said. This is one of the biggest encounters in the Union Territory since April.

"One captain and two soldiers have lost their lives in the ongoing operation in Machil sector. Three terrorists have been eliminated. Operation is underway," Army sources were quoted by ANI as saying.

In a statement, the Border Security Force (BSF) had said constable Sudip Sarkar lost his life during the operation, adding that reinforcements were received from the Army.

In another statement earlier, the Indian Army had said, "Suspicious movement of unidentified persons detected by patrolling party at Machil Sector (J&K) on intervening night of 7 and 8 November. Terrorists trying to infiltrate intercepted; contact established."

Around 1 am, a patrol party of the Border Security Force noticed suspicious movements near the Line of Control and challenged the intruders, leading to a three-hour gun-battle in which a terrorist was eliminated.

The operation is still underway, the official said.

The Indian border troops have had a tough time along international boundaries especially this year with Pakistan and China throwing a two-pronged challenge in tandem along the Line of Control and Line of Actual Control, respectively.