Smoke billows from houses after the bombing of Islamist militant positions in Marawi on September 17, 2017

A Catholic priest kidnapped by Islamic State supporters when they occupied parts of a southern Philippine city nearly four months ago smiled and called for prayers Monday after escaping.

Father Teresito Suganob appeared at a press conference at military headquarters in Manila after he was rescued late on Saturday, when the military said it overran the militants' control centre inside a mosque in Marawi city on Mindanao island.

"Thank you and I pray for you, God bless you all. Pray for me, for my recovery," said Suganob, commonly known as "Father Chito", as he smiled and waved to reporters.

In jocular mood despite his ordeal, the heavily bearded but apparently well-fed Suganob declared: "I am physically strong and handsome. That's it for now."

Hundreds of gunmen rampaged through Marawi, the main Muslim city in the mostly Catholic Philippines, on May 23 and then occupied key districts in what authorities said was an attempt to establish a Southeast Asian base for IS in the Philippines.

More than 800 people have been killed and large parts of Marawi have been destroyed in the ensuing fighting, which has seen the militants defy a US-backed military campaign that has included heavy bombing.

Suganob was taken hostage along with about 13 parishioners from a Marawi cathedral on the first day of the fighting. The militants later released a video showing themselves vandalising the cathedral.

A video released by his captors in late May showed Suganob standing in the rubble of buildings in Marawi asking President Rodrigo Duterte to withdraw troops and stop the military offensive.

Suganob said at the time that the gunmen were holding 240 "prisoners of war", including teachers, carpenters and household workers. They were mostly Christians and local tribespeople.

"We want to live another day. We want to live another month," Suganob said in the video as gunfire was heard in the distance.

One escaped hostage later told authorities that Suganob had been forced to serve as a cook for the militants, according to the then-military spokesman Lieutenant Colonel Jo-ar Herrera in early July.

This was one of many reports that the militants were forcing their hostages to work as slaves.

Authorities said the hostages' roles included carrying the gunmen's food and ammunition, serving as stretcher-bearers for their wounded, collecting munitions and even acting as human shields.

Military spokesman Brigadier General Restituto Padilla said on Monday that 673 militants, 47 civilians and 149 soldiers had been killed in the fighting.

He said there were 40 to 60 hostages still in the hands of the militants, adding some were still being forced to fight on the side of the gunmen.

There were up to 80 fighters on the IS side but they could include some of the hostages, according to Padilla.