The Canadian government has "every reason to believe" that one of its citizens kidnapped by Islamic militants in the southern Philippines nearly nine months ago has been killed, Prime Minister Justin Trudeau said Monday.

Members of the notorious kidnap-for-ransom Abu Sayyaf gang had said they would murder Robert Hall if they did not receive 300 million pesos ($6.5 million) ransom by Monday.

Hall was among four people abducted in September last year from aboard yachts at a tourist resort on Samal island in the southern Philippines. He would be the second Canadian from the group to be killed.

"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 nationally televised address.

"We continue to work closely with the authorities in the Philippines to formally confirm Mr Hall's death. We have every reason to believe that the reports are unfortunately true," Trudeau said.

The Canadian flag atop parliament was lowered to half-mast in Hall's honor.

"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.

After Trudeau's comments, Philippine authorities said late Monday they recovered a human head on the Abu Sayyaf stronghold of Jolo island.

"Yes we recovered a Caucasian-looking one.... Seems like Robert Hall," regional military spokesman Major Filemon Tan told AFP, adding police investigators were now trying to establish the person's identity.

Canadian John Ridsdel was beheaded in April after a similar ransom demand of 300 million pesos was not paid.

The fates of the two other people abducted at the Samal resort -- Hall's Filipina girlfriend Marites Flor and Norwegian resort manager Kjartan Sekkingstad -- were not known.

Norway's foreign minister, Borge Brende, said his country continued to seek their release, while denouncing Hall's killing.

"I condemn in the strongest terms the brutal killing of Canadian citizen Robert Hall. If these reports are true, abhorrence and outrage is the only reasonable response," Brende said in a statement.

- Canada 'will not pay' ransoms -

Listed by the United States as a terrorist organization, the Abu Sayyaf is a loose network of Islamic militants that was founded in the early 1990s with money from Osama bin Laden's Al-Qaeda network.

It is regarded as one of the most radical offshoots of a Muslim separatist insurgency in the south of the mainly Catholic Philippines that has claimed more than 100,000 lives since the 1970s.

The Abu Sayyaf is believed to have just a few hundred armed followers but authorities regard it is as one of the most dangerous terrorist groups in the Philippines.

Its leaders have in recent years declared allegiance to the Islamic State group that holds vast swathes of territory in Iraq and Syria.

But security analysts believe the leaders are chiefly focused on getting money from kidnappings-for-ransom rather than waging a religious war.

Abu Sayyaf gangs have earned many millions of dollars from kidnapping foreigners and Filipinos since the early 1990s.

At a G7 summit in Japan in April, Trudeau pressed partners to publicly denounce such payments, saying it only emboldens hostage takers and fuels more violence and instability.

"Canada cannot and will not pay ransoms to terrorists," he said Monday.

Rather, he said, Canada will continue to work with allies and the Philippines "to pursue those responsible for these heinous acts and bring them to justice, however long it takes."

Aquino vowed after Ridsdel's death that security forces would "neutralize" the Abu Sayyaf, but a fresh offensive involving thousands of troops apparently had little impact.

The Abu Sayyaf has for years withstood repeated military offensives against it, surviving by using the mountainous, jungle terrain and support of local Muslim communities to its advantage.

From 2002-2014, the US deployed Special Forces advisers to train and provide intelligence to Filipino troops, which led to the killing or arrest of many Abu Sayyaf leaders.

But the Abu Sayyaf went on a sustained kidnapping spree after the Americans left.

Source: AFP