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 Moaz al-Kasasbeh "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.
'Ensure safety of Japanese'
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.
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.
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.
The mother of Mr Goto appealed publicly to the prime minister to help her son.
"Please save him," she said. "Kenji has only a little time left."
Analysis: Frank Gardner, BBC security correspondent
The deal being offered by IS, whether genuine or not, goes right to the heart of the universal dilemma over hostage-taking. Do you give in to demands to win the release of your loved ones?
The Jordanian authorities, who were given a final 24 hours on Tuesday to make this decision, find themselves in a dreadful position. IS want the release of a convicted al-Qaeda terrorist from Iraq. To release her could be seen as giving in to terrorism.
Yet at the same time many Jordanians don't support their country's role in US-led air strikes on IS positions. They want their captured pilot to come home alive and for Jordan to stay out of the fight against IS.
Deputy Foreign Minister Yasuhide Nakayama is in Amman negotiating with the Jordanian authorities.
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.
Mr Kasasbeh's father, Safi al-Kasasbeh, told the Associated Press news agency: "The safety of Moaz means the stability of Jordan, and the death of Moaz means chaos in Jordan."
- Formed out of al-Qaeda in Iraq (AQI) in 2013, IS first captured Raqqa in eastern Syria
- It then captured broad swathes of Iraq in June, including Mosul, and declared a "caliphate" in areas it controls in Syria and Iraq
- Pursuing an extreme form of Sunni Islam, IS has persecuted non-Muslims such as Yazidis and Christians, as well as Shia Muslims, whom it regards as heretics
- Known for its brutal tactics, including beheadings of captives and public executions
- The CIA says the group could have as many as 31,000 fighters in Iraq and Syria