Japan's Prime Minister Shinzo Abe attends a lower house committee session at the parliament in Tokyo, January 29, 2015. [Photo/Agencies]

AMMAN/TOKYO  - An audio message purportedly from a Japanese journalist being held by Islamic State militants said a Jordanian air force pilot also held by the group would be killed unless an Iraqi female prisoner in Jordan was released by sunset on Thursday.

The message appeared to postpone a previous deadline set on Tuesday in which the journalist, Kenji Goto, said he would be killed within 24 hours if the Iraqi was not freed.

The latest audio recording, which could not be verified by Reuters, was posted on YouTube early on Thursday. The Japanese government is analyzing the recording, Prime Minister Shinzo Abe told a panel in parliament.

"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 (Iraq) time, the Jordanian pilot Muath al-Kasaesbeh will be killed immediately," the voice in the recording says.

Jordan said on Wednesday it had received no assurance that al-Kasaesbeh was safe and that it would go ahead with a proposed prisoner swap only if he was freed.