Canadian Prime Minister Justin Trudeau has condemned the killing of a Canadian hostage by the Abu Sayyaf armed group in the Philippines, calling it "an act of cold-blooded murder".
Trudeau made the remarks on Monday after the severed head of 68-year-old John Ridsdel was found dumped in a plastic bag on a remote island.
Ridsdel's remains were found five hours after the expiry of a ransom deadline set by the group, who had threatened to execute one of four captives, according to the army.
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Ridsdel, 68, a former mining executive, was snatched by Abu Sayyaf along with three other people in September 2015 while on holiday.
"Canada condemns without reservation the brutality of the hostage-takers and this unnecessary death. This was an act of cold-blooded murder and responsibility rests squarely with the terrorist group who took him hostage," Trudeau said.
"The government of Canada is committed to working with the government of the Philippines and international partners to pursue those responsible for this heinous act."
Trudeau did not respond when asked whether the Canadian government had tried to negotiate with the captors or pay a ransom, or whether it was trying to secure the release of another Canadian being held, Robert Hall.
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"Obviously there was talk of money involved, but not by the government of Canada or by the government of Norway, but certainly by the families attempting to do what they could to free the four," Bob Rae, a former federal politician and longtime Ridsdel friend, told Canadian television.
"But it's been an awful process, just horrendous."
In a statement, Ridsdel's family said they were devastated that his life had been "cut tragically short by this senseless act of violence despite us doing everything within our power to bring him home".
Ridsdel, Hall and the other captives, a Norwegian man and a Filipino woman, had appealed in a March video for their families and governments to secure their release.
Residents found the head in the centre of Jolo town. An army spokesman said two men on a motorcycle were seen dropping a plastic bag containing it.
The army said the al Qaeda-linked Abu Sayyaf had threatened to behead one of the captives if a 300m-peso ($6.4m) ransom for each of them was not paid by 3pm local time.
The initial demand was one billion pesos each for the detainees, who were taken hostage at an upscale resort on Samal Island on September 21.
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Ridsdel's former employer described him as gregarious, adventurous and warm.
"We are in profound shock, disbelief and sorrow to have lost our former colleague and close friend," Calgary-based mining company TVI Pacific said in a statement.
Abu Sayyaf is a small but highly active group known for beheading, kidnapping, bombing and extortion in the south of the country.
It emerged in the early 1990s as an offshoot of a separatist rebellion by minority Moro Muslims in the predominantly Roman Catholic nation's south.
It decapitated a hostage from Malaysia in November last year on the same day that country's prime minister arrived in Manila for an international summit. Philippine President Benigno Aquino has ordered troops to step up their fight against the group.
Security is precarious in the southern Philippines, despite a 2014 peace pact between the government and the largest rebel group that ended 45 years of conflict.
Abu Sayyaf is also holding other foreigners, including one from the Netherlands, one from Japan, four Malaysians and 14 Indonesian tugboat crew.