The captives - two Canadian men, a Norwegian man and a Filipino woman - were kidnapped from a beach resort on a southern island last September.
They are believed to be held in the jungle on Jolo Island, a stronghold of the Abu Sayyaf group, which is known for bombs, beheadings and kidnappings.
THE Abu Sayyaf Group (ASG), a notorious radical terror group in Southern Philippines, had “officially” pledged allegiance to the caliph of the Islamic State of Iraq and Syria (ISIS).
In the video, the captives, with machetes held to their necks, asked their families and governments to pay a ransom of 300 million pesos ($6.51 million) each, down from the figure of a billion pesos each that the militants demanded last year.
"This is already an ultimatum," the masked militant leader said. "We will certainly behead one of these four," he added, setting the execution for 3 p.m. on April 25.
There was no explanation why the ransom was reduced or a new deadline set. A spokesman for the Philippine military declined to comment, saying he had not seen the video. In the nearly two-minute clip posted on Youtube, the foreigners appealed for the militants' demands to be met, R euters reports
"I am told to tell you that my ransom is 300 million," said one man, who identified himself as Robert Hall. "My specific appeal is to the Canadian government, who, I know, have the capacity to get us out of here. I'm wondering what they're waiting for."
The other Canadian and the Norwegian also made appeals, but the Filipino woman was not allowed to speak.
The video was the fourth such appeal released by the ISIS afilliated militants. In their third clip last month, they set an April 8 deadline but no ransom was specified.
Security is precarious in the resource-rich south of the largely Christian Philippines, despite a 2014 peace pact between the government and the largest Muslim rebel group that ended 45 years of conflict.
Abu Sayyaf militants are holding other foreigners, including one from the Netherlands, one from Japan, four Malaysians and 10 Indonesian tugboat crew.
On the nearby island of Basilan, government troops are pursuing another faction of Abu Sayyaf rebels, who killed 18 soldiers and wounded more than 50 in an ambush. The military said 28 militants, including a Moroccan, were killed.
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