KABUL (AFP) - The bodies of three bound and gagged Afghan women were found in a house after a shootout between NATO-backed Afghan forces and insurgents, the military said Friday. It was unclear who killed them but NATOs International Security Assistance Force (ISAF) said it was investigating with Afghan authorities. The gruesome discovery was made late Thursday in Gardez, the capital of Paktia province, in eastern Afghanistan, ISAF said. Fighting erupted after troops raided the building in search of militants. Several insurgents engaged the joint force in a firefight and were killed, ISAF said. Subsequently, a large number of men, women and children exited the compound and were detained by the joint force. When the joint force entered the compound they conducted a thorough search of the area and found the bodies of three women who had been tied up, gagged and killed, it said. The bodies had been hidden in an adjacent room. The bodies of two men were also found in the compound, the force said in a separate statement. A joint Afghan-ISAF investigation, including forensic tests, was underway, ISAF said. The interior ministry of Afghanistan has sent a high-ranking delegation today to jointly investigate this incident, a statement quoted ISAF spokesman Brigadier General Eric Tremblay as saying. Meanwhile, police found the bodies of 20 Taliban militants who froze to death after being driven by troops into the mountains of northern Afghanistan, police said Friday. The bodies were found in two caves deep in snow-covered mountains in Baghlan province on Tuesday, said regional police spokesman Lal Mohammad Ahmadzai. The militants fled into the mountains a day before Afghan and NATO military forces were due to start an operation in central Baghlan, he told AFP. The deputy Taliban shadow governor of Baghlan was among the dead, he said, referring to the militant habit of setting up administrative and justice offices, often in areas that lack any government presence. Police who found the bodies in the caves in the Bysakal area near where three provinces - Baghlan, Kunduz and Takhar - converge also recovered weapons and explosives, Ahmadzai said.