Japan's Prime Minister Shinzo Abe has said a new Islamic State (IS) video threatening to kill hostage Kenji Goto within 24 hours is "despicable".
In the footage a voice believed to be Mr Goto says he and a Jordanian pilot will be killed unless Jordan frees an Iraqi woman held on death row.
Mr Abe said Japan was working with Jordan to secure their release.
IS said on Sunday it had killed another Japanese man, Haruna Yukawa. It had demanded a $200m (£130m) ransom.
In the latest footage, released around midday on Tuesday, the speaker says Mr Goto has "only 24 hours left to live" and Jordanian hostage Mu'ath al-Kaseasbeh "even less" unless Jordan releases Sajida al-Rishawi.
Al-Rishawi is an al-Qaeda militant who has been sentenced to death in Jordan for her involvement in a 2005 attack that killed 60 people.
On Tuesday night, several hundred relatives and supporters of the Jordanian pilot held a protest outside the prime minister's office in Amman, demanding he meet the IS demands.
His father, Safi al-Kaseasbeh, told the Associated Press news agency: "The safety of Mu'ath means the stability of Jordan, and the death of Mu'ath means chaos in Jordan."
The pilot was captured when his plane crashed into IS-held territory in December.
Speaking to reporters at the start of a cabinet meeting on Wednesday morning, Mr Abe said he was appalled by the "utterly despicable" videos, and that the government was asking for Jordanian co-operation.
Japanese Prime Minister Shinzo Abe in parliament (27 Jan 2015)
Mr Abe called on minsters to ensure the safety of all Japanese people abroad
He called on ministers to "take all possible measures to ensure the safety of Japanese nationals at home and abroad," the AFP news agency reports.
Kenji Goto, 47, is a well-known freelance journalist and documentary film-maker who went to Syria in October, reportedly to try to secure the release of fellow Japanese national Haruna Yukawa.
A video appeared on Sunday apparently showing Mr Goto holding a picture of what appeared to be the body of Mr Yukawa.
The BBC's Rupert Wingfield-Hayes in Tokyo says there is growing public support for Japan to do all it can to bring Mr Goto home.
The key question now is whether Jordan will agree to an exchange, he adds. Deputy Foreign Minister Yasuhide Nakayama is in Amman negotiating with the Jordanian authorities.
Our correspondent say there was some optimism on Tuesday that a deal could be reached, but that the latest threat makes it clear that time is short.
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