Tokyo - The Islamic State group's demand that a jihadi on Jordan's death row be exchanged for a Japanese hostage is an attempt to chip away at the US-led coalition against extremism in the Middle East, analysts say.
The militants, whose brutal rule stretches across swathes of Iraq and Syria, is hoping to sow dissent among Jordan, Japan and the United States by offering to spare the life of journalist Kenji Goto.
Their price, they say, is freedom for Sajida al-Rishawi, a woman sentenced to death for her role in the bombing of three hotels in Amman in 2005 that killed 60 people, an event sometimes referred to as "Jordan's 9/11".
And in a chilling development on Tuesday, a new video set a 24 hour deadline for her release, threatening to kill Goto and a captured Jordanian pilot if the militants do not get their way.
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For Tokyo, scarred by the apparent beheading last week of Goto's fellow captive, Haruna Yukawa, it appears to be an attractive offer.
But it leaves Amman trying to balance the demands of a big donor while not losing its best bargaining chip in efforts to secure the release of Maaz al-Kassasbeh, who was captured by Islamic State fighters after they shot his plane down over Syria.
"The Jordanian public would become extremely angry if [Rishawi] were to be released," said Masanori Naito, professor of Islamic studies at Japan's Doshisha University.
That anger would be amplified if Amman played its best hand - releasing Rishawi - only for Tokyo's benefit. "That would deal a serious blow to the Jordanian government. It is a very difficult situation," he added.
It would also risk angering the United States, Japan's bedrock ally and the foundation of its foreign policy, which made clear on Monday that it considered a prisoner swap as "in the same category" as paying a ransom.
"We don't make concessions to terrorists. That remains the case," State Department spokesperson Jen Psaki told reporters.
Jordan, as a moderate Muslim nation, is one of Japan's best diplomatic friends in the Middle East.
On his recent regional tour, Prime Minister Shinzo Abe met King Abdullah II, praising the country's efforts "on the front line of the fight against" Islamic State militants, including its effort to help refugees fleeing war in Syria.
The Japanese premier also announced a fresh $100m loan to Jordan, on top of $28m of assistance to be given via international organisations.
Tokyo turned to Amman when a video emerged last week showing two Japanese men apparently kneeling in the desert as a masked man threatened they would be killed if Japan did not pay a $200m ransom.
Abe dispatched his deputy foreign minister Yasuhide Nakayama to lead Japan's emergency response team from the Jordanian capital, in the hope of leveraging their friendship and opening communication channels to the militants.
But when the jihadists executed one hostage and moved the goalposts with a new demand, it added an unwelcome complication for Amman.
The ISIS move compromises Jordan's position, because it now leaves "Japan applying pressure in the form of the calls to release the death row inmate", according to Japan's biggest-selling paper, the Yomiuri Shimbun.
While Jordan's priority is the return of one of their own, it may quail at disappointing deep-pocketed Tokyo, wary of the possible future impact on relations.
Oraib Rentawi, the director of the Amman-based Al-Quds Centre for Political Studies, said it would be unreasonable for Tokyo to expect the Jordanians to release Rishawi to free Goto while their airman remains captive.
But they may seek to be bold and expand their demands to both captives, he said.
"Now it is an opportunity for Jordan to expand negotiations with ISIS to reach a package deal to release both the Japanese hostage and the Jordanian pilot," he told AFP in Amman.
The Yomiuri Shimbun said a two-for-two swap, which could see Jordan offering another ISIS-related prisoner alongside Rishawi in exchange for both Goto and Kassasbeh, was another possibility.
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The danger, said the newspaper, is that might encourage ISIS to up its demands.
Tokyo on Tuesday seemed to be laying the groundwork for just such a double exchange.
"The release of the Jordanian pilot is an issue for Japan," Nakayama told reporters in Amman, stressing Tokyo's stake in his well-being.
"Both countries are closely cooperating towards the return of each of them to their countries."
But within hours of Nakayama speaking, US Secretary of State John Kerry had telephoned his Japanese counterpart.
Robert Dujarric, director of Asian Studies at Temple University's Tokyo campus, said it was important to remember that Tokyo does not have a completely free hand in cajoling Jordan.
"It also depends on the US position," he said.