An audio recording purportedly from a man being held by IS militants says a fellow hostage has just hours to live unless an Iraqi prisoner is released.

The message, which is unverified, is believed to have been read out by Kenji Goto - a Japanese journalist taken by Islamic State militants last year.

In it the voice demands the release of Sajida al Rishawi, who was sentenced to death in Jordan for her involvement in a 2005 terrorist attack that killed 60 people.

The man states that a fellow hostage - Jordanian pilot Lieutenant Muath al Kasaesbeh - would be killed if the prisoner was not ready to be exchanged at the Turkish border with Syria by "sunset".

The brief message did not make it clear what the fate of either hostage would be even if the group's demands were met.

Japan's chief cabinet secretary Yoshihide Suga said: "We are still in the process of verification but with all of the information gathered we think that there is a high probability that the voice was indeed that of Mr Goto."

Although the Jordanian government is willing to hand over the would-be suicide bomber, nations around the world - including the US - believe the deal with IS should not go ahead.

Such an exchange could set a dangerous precedent, encouraging terrorists to take more people hostage.

However, if both hostages were to survive, it could provide crucial intelligence about their captors, as the whereabouts of a man dubbed "Jihadi John" remains unknown.

The family of Lt al Kaseasbeh have met Jordan's King Abdullah, where they were assured that "things were still positive".

Despite this, the country's Foreign Minister has not received any evidence that the pilot is alive and well.

The Japanese government is investigating the latest footage, which was originally uploaded to YouTube.

The mother of Kenji Goto has made a tearful appeal to Japan's Prime Minister to help save her son.