MANILA • Philippine troops have seized 59 suspected militants attempting to act as reinforcements for Islamist gunmen holed up in the southern city of Marawi, battling government forces for more than two months, military officials said.

The capture of the "suspicious persons" in the troubled Mindanao region has raised questions about how the ISIS-inspired fighters have been able to hold out in Marawi for almost 70 days.

Thirty-two suspected militants were arrested at a military checkpoint in the town of Ipil, while 27 others were taken at a house in Zamboanga City last Tuesday, the regional military spokesman, Captain Jo-Ann Petinglay, said on Friday. A total of 59 police and military uniforms were also seized from the suspects, a military statement added.

The group is suspected of planning to sneak into Marawi to help militants who have been on a rampage since May 23, battling government troops, holding numerous hostages and burning buildings while flying the Islamic State in Iraq and Syria (ISIS) flag.

"They (the troops) have just prevented these individuals from potentially compounding the operational challenges in Marawi should they (have) succeeded in sneaking into the city," a military statement quoted Lieutenant-General Carlito Galvez, commander of the troops in Marawi, as saying.

Capt Petinglay said those arrested were all Filipinos, but their backgrounds were still being checked.

The fighting has so far claimed 630 lives - 471 militants, 45 civilians and 114 government troops, military spokesman Brigadier-General Restituto Padilla said in Manila on Friday.

He told reporters that there were only about 60 militants left, confined to less than one square kilometre of the city.

However, he did not say how much longer the fighting would last.

AGENCE FRANCE-PRESSE