At least three militants were killed as troops foiled an infiltration attempt in Jammu and Kashmir's Kupwara district on Wednesday, a defence official said.Three militants were killed during an ongoing operation near the Line of Control (LoC) in Machil sector of Kupwara, said defence spokesman, Col. Rajesh Kalia.Earlier, a police officer here said that the operation ensued after personnel of the counter-insurgency Rashtriya Rifles, searching the Sardari Nad forests near the LoC on information about presence of militants there, came under gunfire.