Philippine opposition lawmakers yesterday asked the Supreme Court to reject President Rodrigo Duterte's imposition of martial law in the south of the country, branding it unconstitutional.

Duterte declared military rule across the region of Mindanao, home to about 20 million people, on May 23 to quell what he said was a fastgrowing threat from the Islamic State (IS) group there.

Duterte made the declaration a few hours after militants flying black IS flags rampaged through the southern city of Marawi, triggering clashes with security forces that are still ongoing and have left at least 178 people dead.

The petition filed with the Supreme Court yesterday said martial law should be struck down for "utter lack of sufficient factual basis", as it drew parallels with ex-dictator Ferdinand Marcos's military rule a generation ago.

"The grim specter of repression, atrocities, injustice and corruption again bedevils the Filipino people with the unwarranted, precipitate and unconstitutional declaration of martial law," said the petition, filed by six congressmen.

Marcos's two-decade rule ended in 1986 when millions of people took to the streets in a "People Power" revolution.

Thousands of critics, suspected insurgents and their alleged supporters were jailed, tortured or killed during the dictatorship, according to historians.

Shortly after Duterte declared martial law, he praised Marcos's version and vowed his own would be "harsh".

The 1987 constitution imposes limits on martial law to prevent a repeat of abuses under Marcos, including allowing the Supreme Court to review its factual basis.