The message, which has not yet been verified, is currently being analyzed by the Japanese government.

In the audio recording, a voice purporting to be that of Goto states: 'I am Kenji Goto. This is a voice message I've been told to send to you.

'If Sajida al-Rishawi is not ready for exchange for my life at the Turkish border by Thursday sunset 29th of January Mosul time, the Jordanian pilot Mu'ath al-Kaseasbeh will be killed immediately.'

The message was posted on YouTube early this morning.

Air pilot Kaseasbeh was captured by ISIS and along with Goto, is being used as a makeweight for the release of failed suicide bomber al-Rishawi, who is currently imprisoned in Jordan following her involvement in a 2005 bombing.

It was reported yesterday Jordan had agreed to release Sajida al-Rishawi, who was sentenced to death for her part in an Al-Qaeda attack on the Jordanian capital in 2005, in exchange for the pilot.

However, a government spokesman said she was still being held prisoner, while the country's King Abdullah II reassured the pilot's parents things remained 'positive'.

An earlier statement from the country's Foreign Minister said ISIS had not proved the Jordanian pilot was still alive.

At 3pm (GMT) yesterday, Nasser Judeh wrote on Twitter: 'We asked a while ago for proof that hero Maaz (al-Kaseasbeh) is alive but we have not received anything.'

In Jordan, the pilot's father, Safi al-Kasaesbeh, begged the government 'to meet the demands' of the Islamic State group.

'All people must know, from the head of the regime to everybody else, that the safety of Mu'ath means the stability of Jordan, and the death of Mu'ath means chaos in Jordan,' he said.

Jordan's King Abdullah II later met with the pilot's parents and reassured them 'things were still positive', Sky News reported.

Information Minister Mohammed al-Momani said 'Jordan is ready to release the Iraqi prisoner' if al-Kaseasbeh is released unharmed, according to a statement on Jordan's state television. 

Mr al-Momani made no mention of Mr Goto. Mr Judeh later said on his official Twitter account that a Jordanian request for proof that Kaseasbeh was safe and well had gone unanswered.

In separate developments, efforts to free the Japanese journalist were thrown into confusion yesterday after Tokyo was forced to deny reported comments by one of its ministers that a deal was imminent.

The Japanese Deputy Foreign Minister was earlier reported as saying that Mr Goto would be released 'within hours' in a prisoner exchange deal for al-Rishawi.

If this morning's recording proves to be a legitimate threat, this would appear to be incorrect.

Yasuhide Nakayama, who is in Amman to co-ordinate the hostage-release efforts, reportedly said 'good news' was expected in the coming hours, according to Al Jazeera.

Rumours of the imminent release also circulated on other media. However, the claims were quickly denied by the Japanese embassy.

Jordan is reportedly in indirect talks with the militants through religious and tribal leaders in Iraq to secure the hostages' release.  

Earlier, Mr Goto's mother made a tearful appeal to the country's prime minister to save her son. 

Junko Ishido pleaded for Japan's leader to take further action after the militants issued a final death threat in a video on Tuesday.

(dailymail.co.uk)