(Reuters) - An audio message purportedly from Japanese hostage Kenji Goto said a Jordanian air force pilot held by Islamic State militants would be killed unless an Iraqi female prisoner held by the Jordanian authorities was released by sunset on Jan. 29.

The message, which could not be verified by Reuters, was posted on YouTube early on Thursday. The Japanese government is analyzing the purported new voice recording, a spokesman for Prime Minister Shinzo Abe's office said.

"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 Muath al-Kasaesbeh will be killed immediately," the voice in the recording says.