Philippine President Rodrigo Duterte may declare nationwide martial law next week if threatened massive protests by communists and other leftists against his rule turn violent or disrupt the country, his defence chief said Friday.

"He said, if the left will try to have a massive protest, start fires on the streets, they will disrupt the country, then I might (declare martial law)," Defence Secretary Delfin Lorenzana told reporters, recounting a conversation with Duterte this week.

Lorenzana emphasised he thought the chances of Duterte declaring martial law were remote because he doubted the scheduled protests on Thursday next week would be as big as the organisers said they were planning.

"But the president is indeed very concerned because it might get out of hand. So he said I might declare martial law."

A coalition of groups naming themselves the "Movement Against Tyranny" had announced it was planning protests on September 21, the 45-year anniversary of late dictator Ferdinand Marcos imposing his military rule.

It said the protests, to be held at a park in the capital of Manila, would voice opposition against Duterte's war on drugs that has claimed thousands of lives, as well as the president's attacks on democratic institutions.

The coalition also voiced outrage at Duterte's public support for Marcos, who was overthrown in the "People Power" revolution in 1986 and died in US exile three years later.

The announcement for the protest said its theme was: "Stop the Killings! Never Again to Tyranny and Dictatorship!"

Duterte won last year's presidential elections on a brutal law-and-order platform in which he promised an unprecedented campaign to eradicate illegal drugs in society by killing up to 100,000 traffickers and addicts.

Police have reported killing more than 3,800 people in anti-drug operations since he took office 15 months ago, while thousands of others have been murdered in unexplained circumstances.

Duterte has repeatedly threatened to impose martial law across the country, but neither he nor his aides have previously given a specific timeframe or event that would trigger it.

He imposed martial law across the southern third of the Philippines in May after Islamic State group supporters occupied a major Islamic city there, leading to a conflict that has claimed more than 800 lives.

Source: Khaleej Times