IS hostages: Jordan offers prisoner for captured airman
The authorities in Jordan have offered to free a Iraqi prisoner for a Jordanian pilot held by Islamic State after the group threatened to kill the pilot and another hostage.
On Tuesday, IS published a video where a man claiming to be Japanese captive Kenji Goto said Jordan had 24 hours to free the prisoner.
Otherwise both he and Jordanian pilot Moaz al-Kasasbeh would die, he said.
Earlier, IS said it had killed another Japanese hostage, Haruna Yukawa.
It had demanded a $200m (£130m) ransom but there was no mention of the ransom in the new video.
IS has sparked fear and outrage over the past year with its brutal tactics, which include publicly putting to death journalists and soldiers.
Jordan has taken part in US-led coalition air strikes against the group, which began in August. Moaz al-Kasasbeh was captured on 24 December after his plane crashed in northern Syria.
It is hard to see how IS would let both hostages go, BBC world affairs correspondent Paul Adams reports.
That leaves Japan and Jordan in a macabre contest, not of their own making, to get their citizens back, our correspondent says.
Demand for proof
Jordanian government spokesman Mohammad al-Momani said his country was ready to release Sajida al-Rishawi, an Iraqi al-Qaeda militant sentenced to death in Jordan, if Lt Kasasbeh was released and his life spared.
The spokesman did not mention Kenji Goto.
Separately, Jordanian Foreign Minister Nasser Judah said his country had asked IS for proof that the captured pilot was "alive and safe".
Rishawi was convicted in relation to bomb attacks in the Jordanian capital, Amman, in 2005, which killed 60 people.
She was caught with an unexploded suicide bomb belt and confessed to planning an attack with her husband, who was killed.
In the new video, the man who appears to be Kenji Goto says: "Her for me. A straight exchange." There was no indication IS would free the Jordanian pilot, too.
Japanese Prime Minister Shinzo Abe described the new IS video threat as "despicable" and said Japan was working with Jordan to secure the hostages' release.
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.
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, found themselves in a dreadful position. IS wants 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 do not 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.
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 IS demands.
Mr Kasasbeh's father, Safi al-Kasasbeh, told BBC News he did not agree with Jordan being part of the anti-IS coalition.
"When Moath joined the air force he did not join to fight outside Jordan," he said. "He thought he was a Jordanian pilot to defend Jordanian airspace. We never knew that we will be joining other countries to fight outside the Jordanian borders."
- 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