MANILA - The Supreme Court will begin on Tuesday oral arguments on petitions challenging the constitutionality of the extension of martial law in Mindanao until the end of the year.

Four petitions have been filed seeking to invalidate the 1-year extension of military rule in the southernmost island of the Philippines, the second time it was prolonged since President Rodrigo Duterte's initial 60-day declaration in May 2017 due to firefights in Marawi City.

The petitioners include a group of opposition lawmakers led by Albay Rep. Edcel Lagman, members of the Makabayan bloc in the House of the Representatives, former Commission on Human Rights chairperson Etta Rosales, and former Commission on Elections (Comelec) chairman Christian Monsod.

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The high court earlier ordered the consolidation of the petitions, while all parties were asked to submit their memorandum, a pleading that wraps up their arguments, before January 20.

Solicitor General Jose Calida on Monday defended the government's decision to extend martial law anew, saying there is “an ongoing rebellion in Mindanao.”

This in response to the petitioners’ argument that the Islamic State-linked Maute group and its sympathizers who staged a rebellion in Marawi City had been quelled.

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Duterte had cited remaining security threats in Mindanao in seeking another extension of martial law despite the end of hostilities in Marawi City in October.

In December, Congress approved Duterte's request to extend martial law in Mindanao for another year to quell the threat of terrorism.

Lawmakers had previously approved Duterte's first request for an extension of martial law until Dec. 31, 2017.