MANILA - President Rodrigo Duterte's declaration of martial law in all of Mindanao drew divergent views from law experts, with one calling it unnecessary and another saying it should be limited to the conflict-affected area.

President Duterte on Tuesday placed the whole Mindanao island under martial law, after Maute Group and Abu Sayyaf extremists torched buildings and engaged in gun battles with state forces in the southern city of Marawi City.

Christian Monsod, a member of the 1986 Constitutional Commission, said the events in Marawi City do not constitute a rebellion, one of two bases for declaring martial law.

Under the Constitution, the President may declare martial law "in cases of invasion or rebellion, when public safety requires it."

"I don't think that (rebellion) exists at this time. I think this is lawless violence by elements, and that does not involve the purpose of removing from the allegiance to said government or its laws, any part of the territory of the Philippines," Monsod said in a phone interview with ANC.

Monsod said there was no proof that the skirmishes were part of a concerted effort affecting the entire Mindanao.

Declaring a state of emergency, he added, would have been sufficient to address the situation in Marawi.

Ateneo School of Government dean and law professor Antonio La Viña meanwhile said a declaration of martial law was justified, but only in Marawi City and if all online accounts of the terror attack were true.

"If what is being said on social media was true or mainly true, yes. But it only justifies the declaration of martial law in Marawi, not the whole of Mindanao." he told ANC on Wednesday.

Asked if he thinks declaring martial law in Mindanao was an overkill, La Viña said yes, unless the president could prove otherwise through intelligence information that could not be immediately shared with the public.

"I would need to see intelligence that says the problem is Mindanao-wide, island-wide, and that it's serious," he said.

The President should include this information in the martial law report he will be submitting to Congress, as required by the Constitution, La Viña said.

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