Muslim militants in the Philippines have a released a video showing the beheading of Canadian hostage John Ridsdel, an American group that monitors jihadi websites reported Tuesday.

Ridsdel, 68, of Calgary, was one of four tourists -- including fellow Canadian Robert Hall, Norwegian Kjartan Sekkingstad and Filipina Marites Flor -- who were kidnapped last Sept. 21 by Abu Sayyaf militants.

In a series of tweets, Rita Katz of the SITE Intelligence Group cited the video as saying Ridsdel was beheaded on April 25 "due to non-compliance" of the Canadian government.

"The beheading vid...by Abu Sayyaf group is brutal, barbaric, extremely graphic, and most disturbing," Katz said.

Another video released by the militants shows the three remaining hostages, with the militants threatening to behead them if their demands are not met, she said.

The video, obtained by The Canadian Press from SITE, shows the remaining hostages pleading for help with gun-wielding hooded captors behind them. They are seen asking the Canadian and Philippines governments for help.

Ridsdel was beheaded after Abu Sayyaf militants made a large ransom demand for his release.

Prime Minister Justin Trudeau has said Canada would never pay ransom for the release of hostages.

"Paying ransom for Canadians would endanger the lives of every single one of the millions of Canadians who live work and travel around the world every single year," Trudeau said last week.

A senior official said last week that the RCMP was conducting a criminal investigation into Ridsdel's murder. The official, who spoke on condition of anonymity given the sensitivity of the ongoing hostage case, said the Mounties were relying on the extraterritorial provisions of the Criminal Code to pursue the overseas investigation.

The two Canadians, Sekkingstad, who is a permanent resident of Canada, and the Filipina woman were snatched from a marina.

Ridsdel's body was found by villagers beside a dry creek in a mountain near Talipao town in Sulu province. Police recovered his head in Sulu's Jolo town.

Global Affairs Canada advises against all travel to the Sulu Archipelago and through the southern Sulu Sea due to the threat of piracy and kidnappings in this area.

The abductions prompted thousands of Filipino troops to scour Sulu's jungle for the militants, who are believed to be holding about 22 other foreign hostages.

Abu Sayyaf is considered a violent militant group in the southwestern Philippines -- an area beset by a decades-old insurgency -- and has been blamed for several bloody terrorist attacks in the country.