An audio message purportedly from Japanese journalist Kenji Goto has been issued by Islamic State militants who are holding him hostage.
In the audio message, posted on YouTube early on January 29, a voice speaking in English says a Jordanian Air Force pilot held by the militants will be killed if an Iraqi would-be bomber is not released by sunset on January 29.
The voice says, "If Sajida al-Rishawi is not ready for exchange for my life at the Turkish border by Thursday sunset 29th of January Mosul time, the Jordanian pilot Muath al-Kasasbeh will be killed immediately."
Rishawi is on death row in Jordan for her role in a 2005 suicide bomb attack that killed 60 people in the capital, Amman.
The wording of the message does not make clear whether Islamic State (IS) militants intended to release either or both hostages in exchange for Rishawi.
Japan's Chief Cabinet Secretary Yoshihide Suga said the latest video was still being analyzed but that there was a "high probability" the voice was that of Goto.
Suga said the Japanese government was in close communications with the Jordanian government and was working with nations in the region, including Turkey and Israel.
The message appeared to postpone a previous deadline set in a video issued on January 27 in which Goto said he would be killed within 24 hours if the Iraqi woman was not freed.
Goto traveled to Syria in October, reportedly to try to secure the release of Haruna Yukawa, his friend and fellow Japanese national who was captured by Islamic State in August.
In the first of three videos purportedly of Goto, released last week, a black-clad man wearing a mask and holding a knife said Goto and Yukawa would be killed within 72 hours if Japan did not pay IS militants $200 million.
A video on January 24 appeared to show Goto with a picture of a decapitated Yukawa, saying his captors' demands had switched to the release of Rishawi.
Kasasbeh's F-16 fighter jet was downed by IS fighters over Syria on December 24 and his subsequent capture and humiliation by jihadists triggered tensions in Jordan, where the country's involvement in the U.S.-led air raids against IS is controversial.
Jordanian King Abdullah II faces growing domestic pressure to bring the pilot home. The pilot's father said he met on January 28 with the king, who he said assured him that "everything will be fine."
Several dozen protesters gathered on January 28 outside the royal palace in Amman, chanting, "Listen, Abdullah, the son of Jordan [the pilot] must be returned home."
IS militants have carried out massacres and killed several Western hostages execution-style, sometimes on video, after seizing parts of Iraq and Syria in an offensive last year.
A U.S.-led coalition is targeting IS fighters with air strikes as part of what President Barack Obama has called a campaign to "degrade and ultimately destroy" the militant group.