Long battle feared as militants hold on in Philippine city

With bomb-proof tunnels, anti-tank weapons hidden in mosques, human shields and a "mastery" of the terrain, Islamist militants holed up in a southern Philippine city are proving a far tougher opponent than military chiefs expected.

Two weeks after gunmen waving black flags of the Islamic State of Iraq and the Levant (ISIL) rampaged through the Muslim city of Marawi, initial assertions from authorities that the conflict would be over in days have given way to warnings of a protracted battle.

"The advantage of the [enemy] is their mastery of the terrain. They know where even the smallest alleys lead to and they are free to go around," Major Rowan Rimas, an operations officer for the marines, told reporters in Marawi this week.

"They know where the government forces are coming from and where they are taking cover. They have snipers and their positions are well-defended."

Defense Secretary Delfin Lorenzana admitted at the start of the conflict that security forces were taken by surprise when dozens of gunmen appeared on the streets of Marawi following a failed raid to capture one of their leaders.

They emerged from homes in Marawi, the biggest Islamic city in the mainly Catholic Philippines with 200,000 residents, and went on a rampage that included taking a Catholic priest hostage, opening up two jails and destroying many buildings.

Lorenzana and military leaders have since said they unexpectedly interrupted plans by the militants to take over Marawi in a spectacular event to show that ISIL had arrived in the Philippines and was intent on carving out a local territory.

They initially estimated there were about 100 gunmen but later said there were as many as 500, supplemented by foreign fighters including...