TOKYO (AP) — A sunset deadline was approaching Thursday in the Middle East for Jordan to release an Iraqi prisoner or face the death of a captured Jordanian air force pilot, according to the latest threat purportedly issued by the Islamic State group.

The audio message was read in English by a voice the Japanese government said was likely that of Kenji Goto, a Japanese hostage also held by the militant group, which controls parts of Syria and Iraq.

It was released online after Jordan offered Wednesday to hand over the prisoner, an al-Qaida-linked would-be suicide bomber, in exchange for Jordanian air force pilot Lt. Muath al-Kaseasbeh.

The Associated Press could not independently verify the contents of the recording, which was distributed on Twitter by Islamic State-affiliated accounts.

The cases of the Japanese hostage, the Jordanian pilot and the Iraqi prisoner held in Jordan have become intertwined in recent days. The prisoner is Sajida al-Rishawi, a woman convicted of involvement in deadly Amman hotel bombings in 2005.

The recording says the pilot will be killed if the prisoner is not presented at the Turkish border in exchange for Goto's life by sunset. It's not clear what would happen to Goto if the Iraqi woman is not returned by the deadline.

In Tokyo, government spokesman Yoshihide Suga said Thursday the government was in close communications with the Jordan government. He said Japan was doing its utmost to free Goto, working with nations in the region, including Turkey, Jordan and Israel.

"As the situation is developing, I shouldn't comment on details. But, Japan and Jordan are dealing with the matter based on an extremely trusting relationship," Suga told reporters.

Efforts to free al-Kaseasbeh and Goto gained urgency after a purported online ultimatum claimed Tuesday that the Islamic State group would kill both hostages within 24 hours if Jordan did not free al-Rishawi.

Japan has scrambled to deal with the crisis that began last week with the release of a video by the Islamic State group showing Goto and another Japanese hostage, Haruna Yukawa, kneeling in orange jumpsuits between a masked man who threatened to kill them within 72 hours unless Japan paid a $200 million ransom.

That demand has since shifted to one for the release of al-Rishawi. The militants have reportedly killed Yukawa, 42, although that has not been confirmed.

"This heinous terrorist act is totally unforgivable," Prime Minister Shinzo Abe said in parliament Thursday.

Goto, a freelance journalist, was captured in October in Syria, apparently while trying to rescue Yukawa, who was taken hostage last summer.

In Tokyo, Goto's mother, Junko Ishido, has been desperately pleading for the government to save her son.

"I know Mr. Abe is someone who can handle this matter. I trust Mr. Abe and I can do nothing but rely on him," she said.

Releasing the would-be hotel bomber linked to al-Qaida would breach Jordan's usual hard-line approach to the extremists and set a precedent for negotiating with them.

It would also be a coup for the Islamic State group, which has already overrun large parts of neighboring Syria and Iraq. Jordan is part of a U.S.-led military alliance that has carried out airstrikes against the extremist group in Syria and Iraq in recent months.

The Islamic State group has not publicly demanded prisoner releases before and Jordan's main ally, the United States, opposes negotiations with extremists.

Jordanian King Abdullah II faces growing domestic pressure to bring the pilot home. The pilot's father said he met on Wednesday with Jordan's king, who he said assured him that "everything will be fine."

The pilot's capture has hardened popular opposition among Jordanians to the air strikes, analysts said

"Public opinion in Jordan is putting huge pressure on the government to negotiate with the Islamic State group," said Marwan Shehadeh, a scholar with ties to ultra-conservative Islamic groups in Jordan. "If the government doesn't make a serious effort to release him, the morale of the entire military will deteriorate and the public will lose trust in the political regime."

Jordan reportedly is holding indirect talks with the militants through religious and tribal leaders in Iraq to secure the release of the hostages. In his brief statement, al-Momani only said Jordan is willing to swap al-Rishawi for the pilot. He did not say if such an exchange is being arranged.

The 26-year-old pilot, al-Kaseasbeh, was seized after his Jordanian F-16 crashed in December near the Islamic State group's de facto capital of Raqqa in Syria. He is the first foreign military pilot the militants have captured since the coalition began its airstrikes in August.

Previous captives may have been freed in exchange for ransom, although the governments involved have refused to confirm any payments were made.

The Islamic State group broke with al-Qaida's central leadership in 2013 and has clashed with its Syrian branch, but it reveres the global terror network's former Iraqi affiliate, which battled U.S. forces and claimed the 2005 Amman attack.

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