MANILA - Armed US troops are on the ground near the besieged Marawi City in the Philippines, but they are in a support role and not participating in fighting Islamic State militants, a Philippines military spokesman said on Wednesday.

"There are some U.S. personnel who are operating equipment to provide information on situation awareness to our troops," Brigadier General Restituto Padilla told a news conference.

"I do not know the exact number and the specific mission. They are allowed to carry rifles for self-defense. But they are not allowed to fight, they only provide support," he said.

• US soldiers' role in Marawi limited to 'technical matters,' says AFP

Lieutenant General Carlito Galvez, head of military command in Western Mindanao, earlier said Islamist militants control about 20 percent of Marawi City in the Philippines, refuting a claim by Islamic State that its fighters were still "spread in more than two-thirds" of the town after three weeks of fighting.

On Wednesday, Padilla said Maute fighters are still hiding in 4 barangays in the city.

"Out of the 96 barangays when we started this incident, there are only 4 barangays now that remain as problematic areas, and these barangays are not the whole barangays anymore," he told ANC's Headstart.

The seizure of Marawi has alarmed Southeast Asian nations which fear Islamic State - on a backfoot in Iraq and Syria - is trying to set up a stronghold on Mindanao that could threaten their region.

Almost the entire population of about 200,000 fled after the militants tried to overrun it, but the military believes that beyond the checkpoints now fencing off its main roads there are still some 300-600 civilians trapped or being held hostage.