The death toll in a protracted battle between fighters from to a group linked to the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group and government troops in the southern Philippine city of Marawi has topped 500, the military said.

Brigadier General Restituto Padilla said on Tuesday that 90 of the dead were soldiers and police officers in Marawi City, 800 kilometres south of Manila.

At least 381 of the dead were fighters killed in the fighting, which began on May 23 after government forces attempted to arrest a local leader of the ISIL-allied group, he added.

Speaking from Marawi, Al Jazeera's Yaara Bou Melhem said that while the civilian death toll remains as 39, the military says this figure is expected to increase dramatically.

"There are still parts of the city it has not been able to access where it is feared that civilians were executed," Melhem said.

Government forces haven't been able to retake the besieged areas of the city due to snipers and booby traps in the conflict zone, she added.

READ MORE - Marawi: A scarred city of Philippines

Defence Secretary Delfin Lorenzana denied a local media report that up to 2,000 civilians had been killed in the conflict, and urged the public to avoid sharing such "unverified reports" that could "cause undue alarm, panic and confusion."

"Such information is not only detrimental to our ongoing operations. It also hurts our economy and our international image as a nation," he said in a statement.

Lorenzana also allayed public fears of a prolonged period of martial law, which some legislators have proposed be extended for another five years in the southern region of Mindanao.

President Rodrigo Duterte declared a 60-day martial law in Mindanao to help boost the fight against the militants in Marawi City. The decree is set to expire in 10 days.

Lorenzana said martial law was "an extraordinary power of the president as commander-in-chief that must be resorted to only when warranted by our national security circumstances."

"Our constitution has prescribed limitations precisely to prevent its being abused as it has implications to the country's peace and order, economy, trade, tourism, and our people's way of life," he added.

More than 300,000 civilians have been displaced as a result of the fighting.