Tokyo - Japan on Thursday said a fresh message from Islamic militants threatening to kill Japanese and Jordanian hostages was very likely genuine.
Chief Cabinet Secretary Yoshihide Suga told journalists the recording, which demands the release of a failed suicide bomber, seemed real.
"We are in the process of confirming it but it is highly probable that the voice is (Kenji) Goto's," he said.
Tokyo is pleading with Amman to help rescue Goto, a journalist who was taken hostage by the Islamic State group.
In their new message posted early Thursday Japan time, the militants demanded that Amman hand over by "sunset" female jihadist Sajida al-Rishawi, who is on death row in Jordan for her role in 2006 triple hotel bombings in Amman that killed 60 people.
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It said the exchange should take place at the Turkish border.
Suga said that Japanese Prime Minister Shinzo Abe had asked "various countries, including Turkey... for their cooperation".
The latest message, apparently using Goto's voice, ordered Jordan to release Rishawi in exchange for Goto's life, and said the group would kill captive Jordanian pilot Maaz al-Kassasbeh if they did not get what they wanted.
Jordan offered Wednesday to release Rishawi in exchange for the airman, whose release Amman has been negotiating since his capture in December.
Japan has been seeking Jordan's help in attempting to free Goto particularly since an IS video released at the weekend said another Japanese hostage, Haruna Yukawa, had been beheaded.
After initially setting a $200 million ransom for the release of Yukawa and Goto, the Islamic State group, which rules swathes of Syria and Iraq, changed tack and demanded Jordan free Rishawi.