The Philippine military chief says three Malaysians, an Indonesian, and possibly Arab fighters have been killed in a southern city that armed groups planned to burn entirely in an audacious plot to project the lethal influence of ISIL.

General Eduardo Ano told the Associated Press in an interview on Tuesday that the military had made advances in containing the week-long siege of Marawi city. He said a top Filipino fighter is believed to have been killed and the leader of the attack was wounded.

Ano said the group plotted to set Marawi ablaze and kill as many Christians in nearby Iligan city on Ramadan to mimic the violence seen by the world in Syria and Iraq.

The army insists the drawn-out fight is not a true sign of the group's strength, and the military has held back to spare civilians' lives.

"They are weak," Ano said of the gunmen, speaking at a hospital where wounded soldiers were being treated. "It's just a matter of time for us to clear them from all their hiding places."

As of Tuesday morning, he said the military working house-by-house had cleared 70 percent of the city and the remaining fighters were isolated.

Still, the fighters have turned out to be remarkably well-armed and resilient.

Attack helicopters were streaking low over Marawi on Monday, firing rockets at hideouts, as heavily armed soldiers went house to house.

The gunmen have held the Philippine army at bay, burning buildings, taking at least a dozen hostages and sending tens of thousands of residents fleeing.

Ano said Tuesday that the commander, Isnilon Hapilon, is still hiding somewhere in the city. Authorities were working to confirm that another leader had been killed.

President Rodrigo Duterte declared martial law in the south through mid-July after the fighters went on a deadly rampage in Marawi last week following an unsuccessful military raid to capture Hapilon.

In recent years, small armed groups in the Philippines, Indonesia and Malaysia have begun unifying under the banner of Islamic State of Iraq and the Levant (ISIL). Jose Calida, the top Philippine prosecutor, said last week that the violence on the large southern island of Mindanao "is no longer a rebellion of Filipino citizens".

Rohan Gunaratna, a security expert at Singapore's S Rajaratnam School of International Studies, said ISIL and the smaller regional groups are working together to show their strength and declare a Philippine province part of the caliphate that ISIL says it created in the Middle East.

READ MORE: Philippines - Hundreds trapped in battle for Marawi

He said the fighting in Marawi, along with smaller battles elsewhere in the southern Philippines, may be precursors to declaring a province, which would be "a huge success for the terrorists".

Last week, two suicide bombings in Jakarta, Indonesia, killed three police officers, an attack claimed by ISIL. While Indonesia has been battling local fighters since 2002, the rise of ISIL has breathed new life into those networks and raised concern about the risk of Indonesian fighters returning home from the Middle East.

Analysts have warned that as ISIL is weakened in Syria and Iraq, battered by years of American-led attacks, Mindanao could become a focal point for regional fighters.

Southeast Asian fighters fleeing the Middle East "could look to Mindanao to provide temporary refuge as they work their way home", said a report late last year by the Jakarta-based Institute for Policy Analysis of Conflict, predicting a high risk of regional violence.

Marawi is regarded as the heartland of the Islamic faith on Mindanao island.

Muslim rebels have been waging a separatist rebellion in the south of the predominantly Roman Catholic nation for decades. The largest armed group dropped its secessionist demands in 1996, when it signed an autonomy deal with the Philippine government. Amid continuing poverty and other social ills, restiveness among minority Muslims has continued.

Hapilon is an Islamic preacher and former commander of the Abu Sayyaf group who pledged allegiance to ISIL in 2014. He now heads an alliance of at least 10 smaller groups, including the Maute.

Acmad Aliponto, a 56-year-old court sheriff who decided not to flee the city, said while the fighters were well-armed, he believes they have little local support, and that the recent violence could turn more people against them.

"In the end their relatives and everyday people may be the ones who will kill them," he said. "Look at what they did. So many were affected."