In the audio message, al-Qaeda's number two charged that Egypt and Saudi Arabia were planning to join an "offensive" against Hamas, which seized Gaza 10 days ago from the secular Fatah party of president Mahmud Abbas.

And in a dramatic change of tone, Zawawhiri urged Muslim fighters to back Hamas with funds and weapons, saying it was a "religious duty."

"Today we must support the Mujahedeen (holy warriors) in Palestine, including the Hamas Mujahedeen, despite all the mistakes made by their leadership," Zawahiri said on the Al-Hasbah site often used by al-Qaeda.

"Unite with all the Mujahedeen of the world against an offensive being prepared... which the Egyptians and Saudis will join in," he said.

Zawahiri, who in the past spoke out vehemently against the Islamic Resistance Movement (Hamas) for joining the political process in the Palestinian territories, urged the group to amend its policies.