Mustafa Abu al-Yazid presented himself as the leader of al-Qaeda in Afghanistan.
In the tape, sections of which were aired on Thursday, al-Yazid said that al-Qaeda fighters would soon carry out attacks, and that al-Qaeda's Arab fighters were working "side by side" with its non-Arabs fighters.
He said: "The number of fighters is increasing. The support they receive from Muslims in Afghanistan is almost total."
He said that attacks against "the Americans, Nato and the treasonous government" were increasing and promised "defeat, expulsion and failure for the enemy crusaders and their apostate helpers".
He also pledged allegiance to Osama bin Laden, al-Qaeda leader, and Ayman al-Zawahiri, bin Laden's deputy.