Philippines troops thwarted an original plan drawn up by the militants now holed up in Marawi City to "spread terror" in a rampage of violence that would have given them full control of the southern town, the military said on Wednesday.

"There was indeed a bigger plan and it was supposed to wreak more havoc," military spokesman Restituto Padilla told a news conference as aerial bombing resumed against fighters who have sworn allegiance to the ultra-radical IS militant group. 

Philippine senators said members of the upper house were last week shown a video of the militants, led by a group known as Maute, plotting a far more sophisticated siege of Marawi City than the attack they launched there on May 23.

"It was clear that these terrorists, the Maute group, their end goal is to make Marawi... independent, or to separate from the republic," Senator JV Ejercito told Reuters.

"With a plan like this, this is already rebellion and a threat to national security, so declaration of martial law is justified," he said, referring to the martial law declared by President Rodrigo Duterte across the southern island of Mindanao when the siege began.

The Associated Press (AP) first reported on the seized video footage, which showed Isnilon Hapilon - proclaimed last year by IS as its "emir" of Southeast Asia - and others planning to take hostages from a school, seal off roads and capture a highway.

Armed forces Chief of Staff General Eduaro Año told the AP that the images showed an intention to dismember "a portion of the Philippine territory by occupying the whole of Marawi City and establishing their own Islamic state or government".

The battle for Marawi City has raised concern that IS, on a back foot in Syria and Iraq, is building a regional base on Mindanao that could pose a threat to neighbouring Indonesia, Malaysia and Singapore too.

Officials said that, among the several hundred militants who seized the town, there were about 40 foreigners from Indonesia and Malaysia but also fighters from India, Saudi Arabia, Morocco and Chechnya.

The military has said that the fighters are increasingly penned in around a built-up area of the town, and troops have been clearing houses that the militants had defended with snipers for the past two weeks.

The fighters prepared for a long siege, stockpiling arms and food in tunnels, basements, mosques and madrasas, or religious schools, military officials say.

Progress in the military campaign has been slow because hundreds of civilians are still trapped or being held hostage, some as human shields, the military said.

A Catholic priest and about a dozen of his parishioners were taken on the first day of the battle by militants who burst into the town's cathedral and set it alight.

Military spokesman Padilla appealed to social media users not to circulate material, such as the razing of the church, that may fan religious tensions.

"Let us not buy into the plan of these terror groups to inflame the feelings of our other religions," he said. "This is not a religious war."

A four-hour ceasefire to evacuate residents trapped in the town was interrupted by gunfire on Sunday, leaving some 500 to 600 inside with dwindling supplies of food and water.

Officials say that 1,545 civilians have been rescued.

The latest numbers for militants killed in the battle is 134, along with 39 security personnel. The authorities have put the civilian death toll at between 20 and 38.

Source: Timesofoman