Philippine President Rodrigo Duterte yesterday ruled out negotiations with Muslim militants still occupying parts of the southern city of Marawi, amid reports that civilians held as hostages are being forced to serve as sex slaves, take up arms against government troops and loot homes.

"For what (the militants) have done, there will be no quarter given, and no quarter asked," Mr Duterte, making his first public appearance after a week-long absence, said at an event to mark the end of the Eid al-Fitr Islamic holiday.

He spoke of the misery faced by civilians in the conflict.

"I am not happy that you are suffering. I don't see satisfaction even in winning the war. I just want this thing over, and those radicals, extremists out of the Muslim world," said Mr Duterte.

His spokesman, Mr Ernesto Abella, said earlier in the day that the government's policy not to negotiate with terrorists remains.

"Let us continue to remind the public that the gravity of the terrorists' and their supporters' offence is immense, and they must all be held accountable for all their actions," said Mr Abella.

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The Philippine Daily Inquirer reported yesterday that Abdullah Maute, who led the assault on Marawi last month, told religious emissaries on Sunday he wanted his parents freed in return for Father Teresito Suganob, the vicar- general of Marawi.

Fighting has raged in Marawi since an operation to arrest the militant Isnilon Hapilon went wrong on May 23. Hapilon was designated by Islamic State in Iraq and Syria (ISIS) as head of its South-east Asia wing.

Taking advantage of a short truce on Sunday to mark Eid al-Fitr, eight Muslim leaders entered the conflict zone alongside rescue teams and briefly met Maute.

But Mr Abella said these emissaries had no authority to bargain with Maute.

The military said the militants holed up in Marawi were fighting among themselves over money and decision-making. Most of the group's leaders have either been killed or have fled, and some fighters were executed for attempting to withdraw from Marawi, the military added.

Hapilon, who with the Maute brothers and top Malaysian terrorist Mahmud Ahmad plotted to occupy Marawi and declare it an ISIS "province", had already slipped away from the conflict zone, a military spokesman said.

Yesterday, the army reported that civilians held hostage by the militants have been forced to convert to Islam, carry wounded fighters to mosques and marry militants.

"So they are being forced to be sex slaves, forced to destroy the dignity of these women," according to Lieutenant Colonel Jo-Ar Herrera.

He added: "So this is what is happening inside, this is very evident... these are evil personalities."

The army also reported that it has cut off a water route being used as a "logistical and medical highway" by the militants following the arrest of a man who had used a boat to smuggle ammunition into the battle zone and ferry wounded militants out.

Defence Secretary Delfin Lorenzana yesterday said security officials were hoping to retake Marawi before Mr Duterte delivers his State of the Nation address on July 24.

He added that General Eduardo Ano told him the battle would be fierce as the militants had vowed to "fight to the death", but that it should be over in a week or two.