Philippine President Rodrigo Duterte has threatened to jail critics of his use of martial law in the south, as the Supreme Court is set to rule on its legality on Tuesday.

Duterte declared military rule across the region of Mindanao, home to about 20 million people, in late May to quell what he said was a fast-growing threat from the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group.

The president has insisted he would ignore the findings of the country's highest court, which has constitutional oversight, vowing only to listen to recommendations from the armed forces.

"It's not dependent on the whim of the Supreme Court. Should I believe them? When I see the situation is still chaotic and you ask me to lift it? I will arrest you and put you behind bars," Duterte said in a speech before local officials on Saturday.

"We can talk of anything else and make compromises, maybe, but not when the interest of my country is at stake."

READ OPINION: Duterte's reality check in Mindanao

Government forces are continuing to battle ISIL-linked fighters occupying the southern city of Marawi, with aerial bombardment and ferocious street-to-street combat that has left some 400 people dead and forced nearly 400,000 people in the wider area to flee their homes.

Duterte has faced a backlash from opposition politicians, who last month asked the Supreme Court to reject the declaration of martial law, which they have slammed as unconstitutional.

The 1987 Constitution of the Philippines imposes limits on martial law to prevent a repeat of the abuses under Ferdinand Marcos, who was deposed by a famous "People Power" revolution the previous year.

The charter allows the Supreme Court to review the factual basis for proclaiming martial law, which is limited to an initial period of 60 days. If a president decides to extend martial law, Congress can review and revoke it.



