The Islamic State group has released a new message purportedly from its reclusive leader, claiming his self-styled "caliphate" is doing "well" despite an unprecedented alliance against it.

Abu Bakr al-Baghdadi said in a 24-minute audio message posted on Boxing Day that airstrikes by the international coalition only increase his group's determination and resolve.

He also mocks a recently-announced Saudi-led Islamic alliance against "terrorism" and warns Israel that "we are getting closer to you" every day.

To Israeli Jews, he says they "will hide behind trees and stones" from IS.

Al-Baghdadi urges Muslims to join the fight the world over, saying it is their Islamic duty to rise up.

The authenticity of the audio could not be independently confirmed but it was posted on IS-affiliated websites and Twitter as past IS messages.

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