Robert Hall was one of four people kidnapped by the group last September in the southern Philippines. His execution follows that of fellow Canadian hostage John Ridsdel
on April 25 when the militants did not receive the requested ransom.
"We strongly condemn the brutal and senseless murder of Mr. Robert Hall, a Canadian national, after being held captive by the Abu Sayyaf group in Sulu for the past nine months," the statement from Sonny Coloma, a Presidential spokesperson.
Canadian Prime Minister Justin Trudeau said Monday that it was likely Hall had been executed: "It is with deep sadness that I have reason to believe that a Canadian citizen, Robert Hall, held hostage in the Philippines since September 21, 2015, has been killed by his captors," Trudeau said in a statement, adding that officials were working to officially confirm his death.
"The vicious and brutal actions of the hostage-takers have led to a needless death. Canada holds the terrorist group who took him hostage fully responsible for this cold-blooded and senseless murder," Trudeau said.
Severed head 'found in plastic bag'
The Philippines military said the head of a Caucasian-looking man was found in a plastic bag near a church in the town of Jolo, off the southern island of Mindanao late Monday, hours after they received intelligence reports that Hall was decapitated by the Abu Sayyaf.
The militant group originally asked for 300 million Philippine pesos ($6.5 million) in ransom per hostage to be paid by April 25.
The two Canadian men -- along with Hall's Filipina partner, Marites Flor, and Norwegian national Kjartan Sekkingstad -- were taken in a raid on the Oceanview Resort on Samal Island, which lies off the coast of the southern island of Mindanao.
Hall, Ridsdel and Flor were visiting the resort's marina on their yacht, while Sekkingstad was the manager of the property.
The apparent execution comes after Abu Sayyaf released a "final" video of the three hostages pleading with Filipino President-elect Rodrigo Duterte and their embassies for assistance.
The video showed Flor wearing a headscarf, Hall and Sekkingstad addressing Duterte in a local dialect, according to jihadist monitoring group SITE Intelligence.
The hostage situation is seen as a test of Duterte's pledge to crack down on militant activity.
Even though he has not yet been inaugurated, Duterte apologized to Canadian Prime Minister Justin Trudeau over Ridsdel's execution, vowing to crack down on militancy in his country.
"You can rest assured that when the time comes, we will be able to apprehend the criminals and exact justice," he promised Trudeau.
Some members of Abu Sayyaf pledged allegiance to ISIS in 2014, though the connection between the groups remain tenuous.
In the video, however, the male hostages were pictured wearing orange T-shirts, mirroring ISIS videos in which hostages are forced to wear orange jumpsuits in a grim reference to prisoners at Guantanamo, the U.S.' controversial military prison in Cuba.
Trudeau said that Monday marked "yet another difficult day for Canada and for Canadians as we grieve as a nation for the loss of both John Ridsdel, who was killed on April 25, and Robert Hall."
"With the tragic loss of two Canadians, I want to reiterate that terrorist hostage-takings only fuel more violence and instability. Canada will not give into their fear-mongering tactics and despicable attitude toward the suffering of others," Trudeau said.
"On behalf of the Government of Canada and all Canadians, I would like to express my heartfelt condolences to the family and friends of Mr. Hall. They have suffered a terrible loss, and this is a devastating moment for them."