MARAWI CITY - Armed Forces attack helicopters continued to pound Maute terrorists in Marawi City on Monday, as seen in this footage taken by ABS-CBN News' Val Cuenca.

Major General Carlito Galvez, head of the military command in Western Mindanao region, on Monday said as many as 200 fighters from the Maute group and others were still inside Marawi, and had made preparations in advance for a drawn-out standoff.

The militants stocked weapons and food in mosques, tunnels and basements to prepare for a long siege, officials said, as the battle for control of the city came to the end of its second week.

"In houses we take over, we see .50 caliber, .30 caliber, and the ammunition are huge. And the Maute, even if they fight two months they will not starve here," he said a news conference.

"If you look at it, there are underground tunnels and basements that even a 500-pounder cannot destroy."

It underlined the level of organization among fighters linked to the Islamic State group, whose ranks of several hundred included foreigners from Indonesia, Malaysia, India, Saudi Arabia, Chechnya and Morocco.

Parrying questions on why the fighters had been able to resist an onslaught from the Philippines army for so long, senior military officers said the main problem was that 500-600 civilians were still trapped in the urban heart of the town.

President Rodrigo Duterte said on Saturday that Marawi City would be fully liberated within three days, but on Monday officials were more circumspect on the timing and gave conflicting estimates of how many combatants were holding out.

The area of the town occupied by the militants had shrunk to less than 10 percent, military spokesman Brigadier General Restituto Padilla told a news conference, adding that the army was pressing on to meet Duterte's deadline but it was not easy.

"Complications have been coming out: the continued use of civilians, potential hostages that may still be in their hands, the use of places of worship ... and other factors that complicates the battle because of its urban terrain," he said.

Military choppers made combat sorties and machine gun fire rattled and smoke billowed in a neighborhood of the town on Monday.

A four-hour ceasefire to evacuate residents was marred by gunfire on Sunday, leaving hundreds of civilians who had hoped to flee the fighting stuck in their homes.

Padilla said that 1,467 civilians had been rescued so far, and the 500-600 still trapped were low on food and water.

"There are places which we use as passageways to enemy territory - when we reach those areas, sometimes we see old people who are weak, cannot move on their own, because of lack of food," he said.

A presidential spokesman said 120 militants have died in the battle, along with 38 government forces. The authorities have put the civilian death toll at between 20 and 38.

Duterte has claimed that the Maute fighters were financed by drug lords in Mindanao. - with a report from Reuters