Philippine President-elect Rodrigo Duterte has apologized to the Canadian prime minister for the beheading of a Canadian by an Islamist militant group, saying he would try to make sure "nothing like this" happens again.

Duterte, 71, has yet to be declared winner of the May 9 election, but an official vote count shows him six million votes ahead of his closest rival, in part because of his campaign of crushing crime, corruption and drug abuse.

"Please accept my apologies for the incident that resulted to the killing of your national," Duterte said on Thursday he told Prime Minister Justin Trudeau who called him up to congratulate him on his election win.

"We will try to see to it that nothing like this will happen again."

Canadian John Ridsdel, a former mining executive, was beheaded by the Abu Sayyaf on the southern island of Jolo on April 25. Trudeau at the time called it "an act of cold-blooded murder".

Another Canadian, a Norwegian and a Filipino woman are still being held captive by the al Qaeda-linked militants eight months after they were abducted in an upscale resort near Davao City, where Duterte was mayor for two decades.

The Abu Sayyaf gave the Philippine and Canadian governments and families of the captives until 3 p.m. on June 13 to pay 300 million pesos ($6.43 million) for the release of each of the captives.

Abu Sayyaf is also holding other foreigners, including one from the Netherlands, one from Japan and four Malaysian tugboat crew.