Philippine authorities say they found the bodies of 16 civilians outside the besieged city of Marawi on Sunday. Government forces have been battling an ISIS-linked extremist group in the area since Tuesday, when the militants seized buildings before torching them and taking hostages. The 16 victims were reportedly found in two separate groups of eight, with one group found with gunshot wounds to the head and their hands tied behind their backs in a ravine outside the city. One of the bodies had a sign attached to it that said “Traitor,” according to Reuters. Jamail C Mangadang, a Marawi police officer, said the executed civilians were laborers pulled off an evacuation bus after being unable to recite verses of the Quran. A separate group of eight victims was found near the Mindanao State University and included women and a child, The New York Times reported. Authorities believe the militant group is trying to win recognition from the so-called Islamic State with its attacks in Marawi, and a militant leader designated as the head of the terrorist group’s network in the Philippines has reportedly been spotted in the area. The ISIS-affiliated Amaq news agency has claimed the terrorist group is responsible for the siege of Marawi, with some extremists declaring the city the “Islamic City of Marawi” online. Battles for the city continued on Sunday, with the government deploying more ground troops and sending air force helicopters to conduct rocket strikes.