Jordan has said it had received no assurance that one of its pilots captured by Islamic State insurgents was safe, and that it would go ahead with a proposed prisoner swap only if he was freed.
The fate of air force pilot Muath al-Kasaesbeh was thought to be tied to that of Japanese hostage Kenji Goto, a veteran war reporter who is also being held by the insurgent group.
However, an audio message late tonight, purportedly from Mr Goto, says Iraqi prisoner Sajida al-Rishawi must be released by sunset on 29 January at the Turkish border or the pilot will be killed.
Reuters said it had not been able to verify the audio recording.
Rishawi is an Iraqi woman who has been on death row since 2006 for her part in triple hotel bombings in Amman that killed 60 people.
Government spokesman Mohammad al-Momani earlier said Jordan was ready to release Rishawi if Mr Kasaesbeh was spared, but made clear that she was still being held until the pilot was freed.
"It's not true she has been released. Her release is tied to freeing our pilot," Mr Momani said. He made no mention of Mr Goto.
Foreign Minister Nasser Judeh said on his official Twitter account that a Jordanian request for proof that Mr Kasaesbeh was safe and well had gone unanswered.
The Jordanian comments have raised concerns in Japan that Mr Goto might no longer be part of any deal between Amman and the Islamic State group.
However, CNN quoted Mr Judeh as saying that "of course" the Japanese hostage's release would be part of any exchange.
Mr Kasaesbeh was captured after his jet crashed in northeastern Syria in December during a bombing mission against IS, which has captured large tracts of Syria and Iraq.
In a video released yesterday, IS threatened to kill Mr Kassasbeh and Mr Goto unless Jordan released Rishawi within 24 hours.
According to Tokyo the deadline expired at about 2pm today.
A small group of demonstrators gathered outside the Royal Palace in Jordan today calling for Jordan to ensure the release of the captured pilot.
They urged the authorities to meet the demands of IS and release Rishawi to save the young pilot's life.
The pilot's father Safi Kasaesbeh said: "I call on all Jordanians to stand as one, calling for the end of Muath's captivity quickly. They have to meet any demand made by Islamic State."
Mr Kasaesbeh was threatened in a video along with the Japanese hostage.
Meanwhile, Japanese Prime Minister Shinzo Abe has described as "despicable" the latest video from the militants.
It was the third video involving the 47-year-old Mr Goto, a veteran war reporter.
Mr Abe reiterated that Japan was calling on Jordan to cooperate in working for Mr Goto's quick release.
He later told parliament that Japan would not give in to terrorism.
The hostage issue is the deepest diplomatic crisis Mr Abe, who must tread a fine line between appearing firm but not callous, has faced in just over two years in office.
"While making every effort to contribute proactively to world peace and stability without giving in to terrorism, we will exert all means to prevent terrorism in our country," Mr Abe told parliament's upper house.
Mother makes emotional appeal
The mother of Mr Goto has begged Mr Abe to save her son's life.
"Dear Mr Prime Minister Shinzo Abe, please save the life of Kenji," said Junko Ishido.
"I call on you to work with all your strength in negotiations with the Jordanian government, until the very end.
"When I see your kind face (Mr Abe), I don't remember what was said, my mind goes blank and all I can do is cry. I beg you Mr Prime Minister Shinzo Abe."
Japanese Foreign Minister Fumio Kishida told reporters earlier that Japan was making every effort in close coordination with Jordan to secure the captives' early release, but he declined comment on the content of those discussions.
Mr Goto went to Syria in late October in order, according to friends and business associates, to seek the release of Haruna Yukawa, his friend and fellow Japanese citizen who was captured in August.
In the first video released last week, a black-clad masked figure with a knife said Mr Goto and Mr Yukawa would be killed within 72 hours if Japan did not pay IS $200 million.
The captor resembled a figure from previous IS videos whose British-accented threats have preceded beheadings.
A video on Saturday appeared to show Mr Goto with a picture of a beheaded Mr Yukawa, saying his captors' demands had switched to the release of al-Rishawi.
"Time is now running very short," the latest video said, with an audio track over a still picture that appeared to show Mr Goto holding a picture of the pilot.
