A severed head that could belong to a Canadian taken hostage by Islamic State-affiliate Abu Sayyaf has been found in the Philippines, according to reports out of Manila.

Prime Minister Justin Trudeau confirmed Monday afternoon that John Ridsdel had been killed, while local media separately reported that a severed head had been discovered by the Philippine military.

Ridsdel was one of two Canadians who were taken hostage last September by Abu Sayyaf, considered by the Canadian Government to be a terrorist organization.

Trudeau said in a press conference Monday afternoon he was "outraged" to hear Ridsdel was killed in "an act of cold blooded murder."

"I am outraged that Canadian citizen John Ridsdel, held hostage since September 21, 2015, has been killed at the hands of his captors," Trudeau said, adding that Canada "condemns without reservation the brutality of the hostage-takers."

Reports from earlier in the day suggested that the Philippines had some optimism about retrieving the hostages from the jungles on Jolo Island, in the country's Sulu province, where the militants are thought to be holding more than a dozen hostages of various nationalities.

The group has repeatedly released videos threatening to kill the hostages if the Canadian Government doesn't fork over a ransom. The videos showed Ridsdel appealing for help at knife and gunpoint alongside other captives Canadian Robert Hall, Filipino woman Teresita Flor and Norwegian man Kjartan Sekkingstad.

GMA News, a local news outlet, reported just before midnight local time that a head was discovered in the town where the captives were believed to be held. The news outlet cites military intelligence as saying that the execution happened, as the kidnappers promised, on Monday afternoon.

The Manila Bulletin reported that the head, wrapped in a plastic bag, was thrown into the street by two men on a motorcycle. They identify the head as Ridsdel's.

"We're told that this is the absolute final warning, so this is a final urgent appeal to governments, Philippine, Canadian, and families, if 300 million is not paid for me by 3 pm on April 25th, they will behead me," said Ridsdel in a video posted online earlier in April.

It's not yet clear whether Canada was negotiating with the hostage-takers. The department of foreign affairs has been quiet on the file, saying that disclosing information could compromise attempts to rescue the hostages.

"This was an act of cold-blooded murder, and responsibility rests squarely with the terrorist group that 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 and bring them to justice.

"On behalf of the government of Canada and all Canadians, I want to express my deepest condolences to the family and friends of Mr. Ridsdel. They have endured a terrible ordeal. This is a devastating moment for all of them. Our thoughts are with them as they come to terms with their loss. I would ask the media to respect their privacy at this difficult time."

"The government of Canada's first priority is the safety and security of its citizens," Trudeau said. The government will not release any information that could compromise the safety of the other hostages at this time, he said.

Photo via Ridsdel's blog

Ridsdel is a former journalist and semi-retired contractor for Calgary-based mining company TVI Pacific. In a photo uploaded to his blog September 20, the day before he was taken hostage, he wears an unbuttoned shirt, sunglasses and a smile, and sits with his hands on the wheel of his boat.

"...[T]he Philippine Islands beckon, and we will be exploring one of the great diving/cruising grounds of the world," he wrote on his blog on August 29. "And do Indonesia next year."

Canada's department of foreign affairs refused comment about Ridsdel's death.

Ridsdel is not the first hostage killed by Abu Sayyaf. Chinese-Malaysian hostage Bernard Then Ted Fen was also beheaded by the group last November.

And in late October, the body of a South Korean man Noi-Sung Hong, taken hostage by Abu Sayyaf in January, was found. The 74-year-old died from an unreported illness.

The Canadian government first listed Abu Sayyaf Group as a terrorist organization in 2003. According to Public Safety Canada, the militant group aims to establish an Islamic state governed by sharia law in the Philippines.

"In practice, however, the ASG primarily uses terrorism for profit: kidnap-for-ransom, guerrilla warfare, mass-casualty bombings and beheadings are particularly favored tactics," Public Safety states.

"The ASG is also responsible for the biggest act of terrorism in Philippine history: in February 2004 the group claimed credit for planting a bomb on a passenger ferry and sinking the vessel, killing more than 100 people."

Abu Sayyaf celebrated the one-year anniversary of its allegiance with ISIS last September.

Following the Paris attacks on November 13, the Malaysian Insider reported that the November 16 internal police memo said there were eight Abu Sayyaf and IS suicide bombers in the state of Sabah, and ten more in the country's capital of Kuala Lumpur.

"These suicide bombers underwent military training in Syria, Afghanistan, and Iraq, as well as prepared to receive orders from their leaders to launch attacks/bombings," the police memo reportedly read.

The report surfaced only days before the APEC Economic Leaders' Meeting, held in the Philippines on November 18 and 19, just after Then's execution. Officials downplayed connections between his beheading and the highly-publicized political event.

According to a December 14 update on the sailing community blog Noonsite.com, the marina has increased security since the hostage-taking, and now a large banner hangs over a railing, displaying the faces of the four hostages above the words: "All looking forward to your freedom."

The author of the update, Luc Callebaut, witnessed the kidnapping at the marina on September 20.

"This banner is symbolic of all of us here missing our [four] friends!" Callebaut wrote. "I really hope to have good news to report very soon!"