In the fourth tape this year, bin Laden hails Abu Musab al-Zarqawi, the slain al-Qaeda leader in Iraq, as a "lion of Islam" and says Americans got the wrong man by convicting Zacarias Moussaoui of involvement in the September 11 attacks.

"I am responsible for assigning the roles of the 19 brothers who took part in the attacks of September 11, 2001," bin Laden said.

The recording appeared on the As-Sahab Internet site that is frequently used by al-Qaeda.

"We will keep up our fight to bleed your money dry, kill your men so that (your forces) go home defeated, as we defeated you in Somalia," bin Laden told US President George W. Bush.

"The banner (of jihad) has not fallen. It will be picked up by another lion of Islam. We will continue our fight against you everywhere, in Iraq, in Afghanistan, in Somalia and in Sudan."

A Central Intelligence Agency official said the tape had been studied and authenticated, but other US officials played down its significance.

"Following a technical analysis of an audiotape (posted) on the Internet, the CIA assesses it is the voice of Osama bin Laden," a CIA official said.

A State Department spokesman said the tape showed that, even though al-Qaeda was getting weaker, "we still have our work cut out for us.

"Their capabilities have been lessened, but they still remain a threat. The fight against al-Qaeda and others who practice terrorism is going to be a long one," deputy spokesman Adam Ereli told reporters.

But White House press secretary Tony Snow said that Bush had little reaction to the latest bin Laden threats.

"No, it's another bin Laden audiotape. It is what it is," he told reporters when asked if Bush had any reaction.