While backing the fight against Israel, al-Zawahri said every Muslim has a duty "to rise up and seek martyrdom and attack and inflict harm on crusaders" in the battle against U.S.-led forces in Iraq and Afghanistan.

He accused Arab countries of turning a blind eye to the Israeli offensive against Hezbollah and the Palestinians.

"My fellow Muslims, it is obvious that Arab and Islamic governments are not only impotent but also complicit ... and you are alone on the battlefield. Rely on God and fight your enemies ... make yourselves martyrs," he said.

Al-Jazeera did not transmit the entire tape, using selected quotes interspersed with commentary from an anchor. The satellite network said the full tape was about eight minutes long and it aired about half of it. Al-Jazeera would not comment on how it received the tape.

The message was al-Zawahri's tenth this year. Bin Laden, al-Qaida's founder, has issued five messages this year.

Al-Zawahri last appeared in a video posted on an Islamic Web site on the anniversary of the London transit bombings.