CAIRO: The Islamic State group threatened on Tuesday to kill two Japanese hostages within 72 hours, demanding a $200 million ransom for their lives from Japan's prime minister as he visited the Middle East.

Prime Minister Shinzo Abe vowed to save captives Kenji Goto and Haruna Yukawa, telling journalists in Jerusalem, "Their lives are the top priority." But with his military generally only operating in a self-defense capacity at home, Abe faced a hard choice of rewarding extremists now targeted by a US-led coalition or asking an ally like America, which has tried a previous hostage rescue in Syria, to launch a risky operation on its behalf.

The video, released via militant websites associated with the Islamic State group and apparently made by its al-Furqan media arm, mirrored other hostage threats it has made. Japanese officials said they would analyze the video to verify its authenticity, though Abe offered no hesitation as he pledged to free the men.

"It is unforgivable," said Abe as he wrapped up a six-day visit to the Middle East. He added, "Extremism and Islam are completely different things."

In the video, Goto and Yukawa in orange jumpsuits with a rocky hill in the background, a masked militant dressed in black standing between them. The scene resembles others featuring the five hostages previously beheaded by the Islamic State group, which controls a third of Iraq and Syria.

"To the prime minister of Japan: Although you are more than 8,000 and 500 kilometers from the Islamic State, you willingly have volunteered to take part in this crusade," says the knife-brandishing militant, who resembles and sounds like a British militant involved in other filmed beheadings. "You have proudly donated $100 million to kill our women and children, to destroy the homes of the Muslims ... and in an attempt to stop the expansion of the Islamic State, you have also donated another $100 million to train the" apostates.

The militant's comments likely refer to money Abe pledged while in Egypt to help Iraq's government and aid Syrian refugees.

Abe and others in his government declined to say on Tuesday whether they'd pay a ransom, though he dispatched Yasuhide Nakayama, a deputy foreign minister, to Jordan to seek the country's support and to resolve the hostage crisis. But agreeing the Islamic State group's demands likely would anger allies like the US, which has a strict policy of not paying ransoms.

UN Secretary-General Ban Ki-moon called for the immediate release of the two Japanese hostages and as well as all other hostages taken by armed groups, especially Islamic State extremists, in Iraq and Syria, UN spokesman Stephane Dujarric said.

Though Abe has said he wants a more-muscular Japanese military, he has ruled out sending troops overseas and Japan's constitution, drafted during the American occupation following World War II, commits the country to pacifism. That would put the onus on partners like the US to attempt a hostage rescue.

American officials had no immediate comment Tuesday. In early July, US special forces launched a secret raid into Syria to free American hostages held by the Islamic State group, killing several militants but finding no captives.

The two Japanese hostages said nothing during the ransom video. Yukawa, a 42 year old who founded a private security company, was kidnapped in Syria in August after going there to train with militants, according to a post on a blog he kept.

Nobuo Kimoto, an adviser to Yukawa's company, told Japanese public television station NHK that he had worried "something like this could happen sooner or later."

Goto, 47, is a respected Japanese freelance journalist who went to report on Syria's civil war last year.

"I'm in Syria for reporting," Goto wrote in an email to an Associated Press journalist in October. "I hope I can convey the atmosphere from where I am and share it."

Tuesday's video marks the first time an Islamic State group message publicly has demanded cash. The extremists requested $132.5 million from Foley's parents and political concessions from Washington, though neither granted them, US authorities say. They asked for a similar amount for two other American hostages, authorities have said.

The Islamic State group has suffered recent losses in US-led airstrikes. With global oil prices being down, their revenue from selling stolen oil likely has dropped. The extremists also have made money from extortion and robbing banks during its August offensive in Iraq.

Greg Ohannessian, an analyst at the Dubai-based Institute for Near East and Gulf Military Analysis, said before the oil-price drop, the Islamic State group made as much as $2 million a day selling oil. That money goes back into payments to pacify the as many as 8 million people living in its self-declared caliphate, he said.

"Now with oil dropping by 60 per cent, that is going to be cutting into their income," Ohannessian said. "That is definitely going to have an impact on their capacity to maintain the population."

It also recently released some 200 mostly elderly Yazidi hostages in Iraq, fueling speculation by Iraqi officials that the group didn't have the money to care for them.

The Islamic State group has beheaded and shot dead hundreds of captives — mainly Syrian and Iraqi soldiers — and has celebrated its mass killings in graphic videos. The group also beheaded American hostages James Foley and Peter Kassig, Israeli-American Steven Sotloff, and British captives David Haines and Alan Henning.

The group still holds British photojournalist John Cantlie, who has appeared in other extremist propaganda videos, and a 26-year-old American woman. US officials have asked that the woman not be identified out of fears for her safety.

This is Abe's second Mideast hostage crisis since becoming prime minister. The first came two years ago when al-Qaida-affiliated militants attacked an Algerian natural gas plant, killing 37 foreigners, including 10 Japanese. Seven Japanese workers survived.

What Abe and others in Japan fear is a replay of 2004, when followers of Jordanian militant Abu Musab al-Zarqawi in Iraq beheaded Japanese backpacker Shosei Koda over Japan having troops in Iraq doing humanitarian work. A video by al-Zarqawi's group, which later became the Islamic State group, showed Koda begging Japan's then-prime minister to save him.