Japan pressed Jordan for help in securing the release of Kenji Goto, a Japanese hostage of Islamic State militants, after a video on Tuesday appeared to show him saying he could be killed in 24 hours.
"Tell the Japanese government to put all their political pressure on Jordan," says the voice on the video, addressing the Japanese people and saying he will be killed unless Jordan frees would-be suicide bomber Sajida al-Rishawi from death row.
Jordanian state television, quoting an army source, said authorities were trying to authenticate the video. It would be the third involving veteran war reporter Goto.
"The relevant agencies are working on verifying the authenticity of the voice recording that is attributed to Daesh," the source said, using an acronym for Islamic State.
The hostage issue is the deepest diplomatic crisis Prime Minister Shinzo Abe has faced in just over two years in office.
Confronting "an extremely severe situation," Abe ordered his government to continue its policy of seeking Jordan's help in releasing Goto, Chief Cabinet Secretary Yoshihide Suga told reporters after a meeting of national security officials.
The voice in the video says another Islamic State captive, Jordanian pilot Muath al-Kasaesbeh, has a shorter time to live than Goto, 47. Some media reports have said a swap of Goto and the pilot for al-Rishawi and another militant prisoner held by Jordan was being discussed.
Reuters could not verify the authenticity of the video but Suga said it appeared to show Goto and the voice resembled that on a video on Saturday that U.S. and Japanese officials have said appeared to be genuine.
Goto went to Syria in late October in order, according to friends and business associates, to seek the release of fellow Japanese Haruna Yukawa, who was captured in August.
In the first video released last week, a black-clad masked figure with a knife said Goto and Yukawa would be killed within 72 hours if Japan did not pay Islamic State $200 million. The captor resembled a figure from previous Islamic State videos whose British-accented threats have preceded beheadings.
A video on Saturday appeared to show Goto with a picture of a beheaded Yukawa, saying his captors' demands had switched to the release of al-Rishawi, an Iraqi woman held by Jordan for her role in a 2005 suicide bombing that killed 60 people in Amman.
"Time is now running very short," the latest video says, with an audio track over a still picture that appears to show Goto holding a picture of the pilot.
"It is me for her. What seems to be so difficult to understand? She has been a prisoner for a decade. And I've only been a prisoner for a few months."
He says further "delays" by Jordan would result in the death of the pilot and then himself.
Kasaesbeh was captured after his jet crashed in northeastern Syria in December during a bombing mission against the militants.
Goto's mother, Junko Ishido, told Japanese public broadcaster NHK: "I think Japan should do all it possibly can" to secure her son's release.