MARAWI CITY • Bodies of what appeared to be executed civilians were found in a ravine outside a besieged Philippine city yesterday, 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 militants linked to the Islamic State in Iraq and Syria (ISIS) on the outskirts of Marawi City while trying to flee clashes, according to the police.

Nine spent bullet casings were found on a bloodstained 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 - a move which the military believes is aimed at winning the Maute recognition from ISIS as a South-east Asian affiliate.

The Maute group, based in Lanao del Sur, is named after two brothers - Omarkhayam and Abdullah Maute - who were students at Islamic schools in the Middle East.

The fierce resistance of the Maute gunmen and the apparent executions of civilians will add to growing fears that subscribers to ISIS' 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 at 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 the predominantly Muslim city.

Some of those trapped in Marawi - estimated to number 2,000 - had called and texted a hotline, pleading with the military to stop the air strikes, according to Mr 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 damage and the people who are affected... It is really massive."

At least 61 militants and 15 security force personnel had been killed as of last 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 the rebels late on Saturday.

Recalling information provided by their manager, Mr Mangadang said the victims were pulled off a truck because they were unable to cite verses of the Quran, the Islamic holy text.

The military said it was possible that there were other victims. "This development validates a series of reports of atrocities committed by the militants earlier," said military spokesman Restituto Padilla.

Meanwhile, Philippine President Rodrigo Duterte told soldiers on Saturday that he will ignore the Supreme Court and Congress as he enforces martial law across Mindanao, following the deadly clashes in Marawi that began last Tuesday.

"Until the police and armed forces say the Philippines is safe, this martial law will continue. I will not listen to others. The Supreme Court, Congress, they are not here," he said.

REUTERS, AGENCE FRANCE-PRESSE