MANILA - Several senators on Tuesday thumbed down the proposal for a third extension of martial law in Mindanao, saying there is no longer a constitutional basis for prolonged military rule in the south.

Martial law was first declared in Mindanao after clashes between government troops and terrorists erupted in Marawi City in May last year and has remained in effect despite the end of gunfights in the Islamic city in October 2017.

Its second extension, which Congress approved on Duterte's request, will lapse at the end of the year.

Senate Minority Leader Franklin Drilon called the move for yet another extension unconstitutional as an "actual rebellion" no longer exists in the region.

"The Constitution is clear that martial law may be declared only in cases of actual rebellion when public safety requires it," Drilon said in a statement.

"There may be threats of rebellion, but what the Constitution clearly requires as a ground for declaring and extending martial law is the presence of actual rebellion," he said.

Senators Francis Pangilinan and Grace Poe echoed Drilon's statements and urged the military to provide evidence that actual rebellion still exists in Mindanao.

"I would like to ask the AFP (Armed Forces of the Philippines), what is their basis for an actual rebellion, nandiyan pa ba ang Maute? Nandiyan pa ba ang ISIS (Islamic State)?" Poe said.

(Is the Maute [terror group] still there? Is the ISIS still there?)

Pangilinan also sought answers about the alleged threat.

"For instance, it should answer the question: How big and wide is the threat in the region that necessitates it to be placed under such declaration?" Pangilinan said.

Pangilinan, also president of the opposition Liberal Party, cautioned against imposing martial law in the region during an election year.

"A region under the control of the military could affect the campaigning of opposition candidates and those not allied with the administration," he said.

Splinter groups and other minor threats in the south can be contained by state forces even without the declaration of martial law, Drilon said.

"I have full confidence in the capability of our military and the police to suppress criminals, rebels and terrorists,” he said.

Armed Forces Chief of Staff Carlito Galvez had said on Monday that he would ask President Rodrigo Duterte to extend martial rule in the southern region for another year because of the "lurking" threat of terrorism.

• Military chief to recommend martial law extension to Duterte

Presidential spokesperson Salvador Panelo then said Duterte would likely heed Galvez's advice.