Screen shot of previous video of the four hostages in the Philippines.

In a fourth and harrowing video released on Friday, two Canadian men held hostage for more than six months in the Philippines begged their government to come to their aid.

"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," John Ridsdel, a former mining executive, said in a video that was seen by various media outlets online before apparently being removed.

In the video, Robert Hall reportedly appeals directly to the Canadian government, which he says "has the capacity to get us out of here. I wonder what they are waiting for."

Canada's foreign affairs department indicated on Friday that it was aware of the video, but declined to comment or say anything that could "compromise ongoing efforts or endanger the safety of Canadian citizens."

Ridsdel was taken hostage from the Holiday Ocean View Samal Resort off the coast of Mindanao on September 21, alongside Hall, Hall's Filipina companion Marites Flor, and Norwegian Kjartan Sekkinstad, who managed the resort.

Previous videos have shown the captives in deteriorating condition, sitting shirtless, often with machetes to their necks as guards, reportedly part of Abu Sayyaf, a militant group with ties to the Islamic State, stood threateningly behind them.

The first public appeal came in October, with Hall reporting that he is "OK" but "in grave danger," and pleading with the Canadian government to pressure the Philippine authorities to stop bombing the region.

In November, the hostages appeared before several militants brandishing an IS flag demanding $100-million in exchange for their release. Then, in March, a masked spokesperson warned that if an April 8 deadline wasn't met, "We will do something terrible against these captives."

The latest demand of 300 million is apparently in pesos, according to the National Post, which comes out to just over $8-million.

"Deadline of warning is over," one of the hostage takers says in the most recent video. "Still, you procrastinate. So now this is already an ultimatum. Once you don't meet the demand, we will certainly behead one amongst this four."