Extremists allied with Islamic State are believed to have executed Filipinos in a besieged southern city of the Philippines because they could not recite Islamic prayers, as the death toll from six days of fighting rose to 100, with dozens wounded.
The bodies of eight men, most of them shot in the head with their hands tied behind their backs, have been found on the outskirts of Marawi, 830 kilometres south of Manila.
Residents who had fled the city told journalists the militants separated Christians and Muslims by those who could recite the prayers and took away those who could not.
Attached to one of the bodies was a sign that said "Munafik" (hypocrite).
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Earlier reports said the militants beheaded a local police chief.
Authorities said on Sunday that 2000 civilians remained trapped in the city that was home to 200,000, as the military intensified air strikes to drive out heavily armed militants from the little known but brutal Maute group.
Many of those trapped sent text messages to authorities begging to be rescued.
But Zia Alonto Adiong, spokesman for the provincial crisis management committee, said it was too dangerous for rescue teams to enter parts of the city.
"Some are running out of food to eat. They fear they will be hit by bullets, by airstrikes," he said.
The military warned in a statement that it was being forced to step-up surgical strikes from combat helicopters.
"In as much as we would like to avoid collateral damage, these rebels are forcing the hand of the government by hiding and holding out inside private homes, government buildings and other facilities," it said.
"Their refusal to surrender is holding the city captive."
The crisis has become dire since about 100 militants rampaged through the city last Tuesday after a botched military raid on the hide-out of Isnilon Hapilon, an Arabic-speaking preacher and combat specialist who is on Washington's most wanted list.
Hapilon's group then called in reinforcements and torched buildings, posted snipers on roof-tops to repel troops and took an unknown number of hostages, including a Catholic priest.
The strength and capability of the militants have reinforced fears of Islamic State gaining a foothold in the southern Philippines, from where it could organise attacks in other parts of south-east Asia.
Authorities say foreigners, including Indonesians and Malaysians, have been among the dozens of militants who have been killed since Tuesday.
Philippine Defence Secretary Delfin Lorenzana told reporters that Hapilon's group had received a "couple of million dollars" from Islamic State.
He did not elaborate.
Philippine President Rodrigo Duterte has imposed martial law across Mindanao, the country's second largest island, and warned the country is at grave risk of "contamination" by Islamic State.
"You can say that IS (Islamic State) is already here," he said.
Philippine military chief Eduardo Ano predicted it would take about a week to clear the city as soldiers go house to flush out the fighters.
Hapilon heads an alliance of 10 militant groups in the southern Philippines who have pledged allegiance to Islamic State.
Washington has offered a US$5 million reward for information leading to his capture.
with agencies