Incendiary Philippine politician Rodrigo Duterte vowed Tuesday a relentless crackdown on crime after securing a landslide presidential victory built on foul-mouthed populist tirades that exposed deep voter anger at the establishment.

The 71-year-old firebrand's main rivals conceded defeat after an unofficial tally showed Duterte had an insurmountable lead in Monday's election of 6.1 million votes, a result that added to howls across the globe for strong, populist leaders.

Mass murder advocate Rodrigo Duterte heads into Saturday's final rallies of an extraordinary Philippine presidential campaign as the shock favorite, but with rivals still a chance to counter his profanity-laced populist tirades.

Duterte, a pugnacious 71-year-old, has rocked the political establishment with cuss-filled vows to kill tens of thousands of criminals, threats to establish one-man rule if lawmakers disobey him, and promises to embrace communist rebels.

Walking off stage after a rock star-like performance and rapturous crowd reaction, Sajid Ampatuan oozes confidence that he will be elected mayor of a southern Philippine town despite facing charges of mass murder.

Ampatuan is among a bewildering array of politicians accused or convicted of major crimes who are running for office in Monday's national elections, deepening concerns over a "culture of impunity" in the Philippines where powerful figures are often above the law.

Philippine President Benigno Aquino vowed Wednesday to launch a military assault aimed at "neutralizing" Islamic militants who beheaded a Canadian hostage and are holding more than 20 other foreigners.

"Casualties are to be expected. But what has to be of utmost importance is neutralizing the criminal activities of the ASG," Aquino said in a statement, referring to the Abu Sayyaf militant group by a commonly used acronym.

Philippine soldiers killed four more militants as they pressed their offensive against the Abu Sayyaf after suffering heavy losses in weekend clashes in the troubled south, authorities said Monday.

Troops killed the four on the strife-torn island of Basilan on Sunday, a day after the guerrillas killed 18 soldiers in the worst fighting so far this year, regional military spokesman Major Filemon Tan said.

The Philippines on Sunday hailed a new accord giving the U.S. military access to five of its bases, saying this would strengthen its defensive capabilities and maritime security.

The agreement between the two close allies comes as the Philippines and other countries are embroiled in a tense dispute with China over conflicting territorial claims in the South China Sea.

The Philippine coastguard said it was closely watching a North Korean vessel and its 21 crew members Sunday, as officials waited for a response from the United Nations days after the ship was seized in compliance with new sanctions.

The 6,830-tonne cargo ship, the Jin Teng, is being held at Subic port, northeast of Manila, where the Philippine coastguard are guarding the freighter and monitoring its crew, said coastguard spokesman Commander Armand Balilo.

At least six people have been killed and more than 20,000 displaced during a week of fighting between Islamic militants and security forces in the southern Philippines, authorities said Friday.

Three soldiers and three militants were confirmed killed in the clashes, which involved followers of a slain Indonesian leader of a Southeast Asian militant group, the military said.

The head of the Philippines' main Muslim rebel group on Thursday urged his followers to maintain a ceasefire with the government despite failure to pass a bill implementing a peace accord.

Moro Islamic Liberation Front (MILF) chairman Murad Ebrahim made the appeal in a statement carried on the group's Facebook page.

Six Philippine policemen were killed and eight injured in an ambush by communist rebels on a remote mountain highway on Tuesday, the military said.

Around 40 communist guerillas strafed a police convoy in Baggao, a poor farming town in the northeast of the main island of Luzon, sparking a brief firefight, said a regional military spokesman.