Eight civilians were found dead in a ravine outside a besieged city in the southern Philippines, according to a Sunday Reuters report.

The departed were part of an evacuation convoy stopped by Muslim militants with ties to the Islamic State. The men were bound and shot in the head after they failed to recite scripture from the Quran, Marawi police officer Jamail C. Mangadang revealed, according to Reuters.

The discovery of the bodies confirms earlier reports that the militants who have taken over the city of Marawi are slaughtering civilians. They also beheaded the police chief, torched schools and churches, and raised the black ISIS standard over government facilities. The militants also liberated inmates from local prisons, while taking Christians as hostages.

EXCLUSIVE: Maute Group slaughtered 9 civilians after they were flagged down at a checkpoint manned by terrorists in Marawi | @jun_veneracion pic.twitter.com/1QETDAqKez — GMA News (@gmanews) May 24, 2017

A sign with the word “traitor” written on it was found beside the bodies.

The military reported that there may be other victims. “We are still validating other reports of atrocities,” military spokesman Restituto Padilla told reporters.

An intense battle is being waged in Marawi and has been for six days. The fighting began Tuesday when government security forces attempted to bring down Abu Sayyaf leader Isnilon Hapilon, who is a high-profile terrorist target believed to have direct ties to ISIS. The raid quickly evolved into a major firefight as Hapilon’s forces called for reinforcements from the Maute Group, another ISIS-linked insurgency operating in the area.

The Islamic State claimed responsibility for Maute’s siege, declaring the town the “Islamic City of Marawi.” Government officials claim they have received over 2,000 distress calls from civilians trapped in militant-controlled areas. Tens of thousands of residents have fled the city to escape the destruction.

President of the Philippines Rodrigo Duterte has declared martial law in the southern Philippines in response to what he referred to as a rebellion and efforts by ISIS to establish a permanent foothold. The military has been sending in tanks and assault vehicles while conducting airstrikes against militant positions.

Fifteen Filipino soldiers lost their lives to the fight, but they took over 60 militants with them.

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