MARAWI CITY, Philippines (Reuters) - Bodies of what appeared to be executed civilians were found in a ravine outside a besieged Philippine city on Sunday as a six-day occupation by Islamist rebels fending off a military onslaught took a more sinister turn.
The eight dead, most of them shot in the head and some with hands tied behind their backs, were labourers who were stopped by Islamic State-linked militants on the outskirts of Marawi City while trying to flee clashes, according to police.
Nine spent bullet casings were found on a blood-stained patch of road at the top of the ravine. Attached to one of the bodies was a sign that said "Munafik" (traitor).
The discovery confirms days of speculation that Maute rebels had killed civilians during a takeover of Marawi, that the military believes is aimed at winning the Maute recognition from the Islamic State as a Southeast Asian affiliate.
The fierce resistance of the Maute gunmen and the apparent executions of civilians will add to growing fears that subscribers to Islamic State's radical ideology are determined to establish a presence in the southern Philippines, with the support of extremists from Indonesia and Malaysia.
The army deployed more ground troops over the weekend and dispatched army and air force helicopters to carry out rocket strikes on Maute positions as fighters held buildings and a bridge deep inside a predominantly Muslim city where few civilians remained.
Some of those trapped in Marawi had called and text-messaged a hotline pleading with the military to stop the air strikes, according to Zia Alonto Adiong, a local politician coordinating complex efforts to evacuate civilians, dead and alive.
"Some have no food at all. Some fear for their lives," he told Reuters.
"This is a conflict that has gone beyond proportion. The magnitude of the degree of the damage and the people that are affected ... it's really massive."
At least 61 militants were killed and 15 security forces as of Saturday, according to the army, which said it could confirm nine civilians killed by militants.
At the ravine where the bodies were found, Marawi police officer Jamail C Mangadang said the victims were carpenters who were part of an evacuation convoy stopped by rebels late on Saturday.
Recalling information provided by their manager, Mangadang said the victims were pulled off a truck because they were unable to cite verses of the Koran, the Islamic holy text.
The military said it was possible there were others victims.
"This development validates a series of reports of atrocities committed by the militants earlier," said military spokesman, Restituto Padilla.
"We are still validating other reports of atrocities."
Islamic State's Amaq news agency last week claimed responsibility for the Maute's brazen siege. Unverified statements claiming to be from the extremists have appeared online, declaring the city of 200,000 people the "Islamic City of Marawi".
President Rodrigo Duterte on Sunday cancelled a trip to Japan to address the unrest in Mindanao, an island of 22 million people where martial law has been declared. Police on Sunday outlawed guns there and suspended all weapons permits.
Fierce battles took place on Sunday as ground troops engaged Maute fighters with heavy gunfire and artillery. Plumes of smoke were seen on the horizon and helicopters unloaded rockets on rebel positions.
A surveillance drone circled the sky above Marawi. Some civilians tied white cloths to poles to distinguish themselves from militants as soldiers on foot huddled behind armoured vehicles that crawled along deserted streets.
Tens of thousands of people have fled Marawi since Tuesday, when militants went on the rampage seizing a school, a hospital, and a cathedral, where Christians were taken hostage, according to church leaders. Scores of prisoners, among them militants, were freed when rebels took over two detention facilities.
The violence erupted in response to a failed attempt by security forces to capture Isnilon Hapilon, who the government believes is Islamic State's point-man in the Philippines.
The military is certain the Maute are protecting Hapilon and had narrowed down his location. Hapilon leads a radical faction of another Mindanao-based group, the Abu Sayyaf.
The little-known Maute group has staged several days-long sieges on Mindanao island but none on the scale of Marawi, where witnesses said flags resembling those of Islamic State had been flown and some gunmen wore black headbands.
The Maute group was blamed for last year's bombing in the president's home city, Davao, which killed 14 people, and its battlefield capability has been a serious challenge to a military that has far larger numbers and firepower.
Another concern for the government was the discovery of Indonesian and Malaysian fighters with the Maute, which it said showed a domestic rebellion had expanded to become a far greater threat, driven by radical ideology.
Reporting by Tom Allard; Additional reporting by Erik De Castro in MARAWI and Manuel Mogato in MANILA; Writing by Martin Petty; Editing by Michael Perry