The Islamic State group has vowed to turn to Israel as the main target of its attacks, according to a purported audio message of its spokesman released on Monday.

Abu Hamza al-Quraishi said IS leader Abu Ibrahim al-Hashimi al-Quraishi encourages the group's fighters to launch "a new phase" and vowed major operations against Israel.

"The eyes of the soldiers of the caliphate, wherever they are, are still on Jerusalem," the spokesman said in the 37-minute message.

"And in the coming days, God willing, you will see what harms you and what will make you forget the horrors you have seen," Abu Hamza al-Quraishi said, apparently threatening attacks of unprecedented scope.

AFP could not immediately authenticate the message but the recording was published via the group's usual social media channels.

The jihadist organisation once administered a sprawling self-proclaimed "caliphate" straddling big parts of Syria and Iraq, where it minted a currency, levied taxes and ran school curricula.

Under pressure from combined military operations by Syrian and Iraqi forces supported by their respective allies, the proto-state collapsed last year.

IS has remained a potent outfit in its Euphrates heartland and surrounding desert hideouts however and its franchises in Africa and Asia have also continued to expand their attacks.

The group also has a presence in Egypt's Sinai peninsula, which borders Israel and which the Jewish state occupied for 15 years after the 1967 war.

The spokesman said IS leader Quraishi was "determined, and has encouraged his mujahideen brothers in all provinces, and Muslims across the world," to launch "a new phase".

That new focus "is fighting the Jews and reclaiming what they have stolen from the Muslims, and this cannot be reclaimed except through fighting," he said.