An audiotape from a shadowy terrorist linked to Al Qaeda is "probably authentic," marking the first time Abu Musab al-Zarqawi (search) has made a taped public statement, a CIA official said Wednesday.

The 33-minute audiotape, calling for Iraq's Sunni Muslims to fight Shiites and claiming responsibility for high-profile attacks there, appeared Tuesday on a Web site known for distributing militant Islamic messages. The speaker introduced himself as al-Zarqawi, a Jordanian believed to be running a terrorist network that stretches from Europe to Central Asia.

Also known as Ahmed al-Khalayleh, al-Zarqawi is also thought to be a close associate of Usama bin Laden (search) and has ties to terrorist groups ranging from Ansar al Islam (search) in Iraq to Egyptian Islamic Jihad (search). He's believed to be behind many attacks in Iraq, including at least a dozen high-profile operations.

"The CIA's assessment is that it is probably authentic," said an agency official, speaking on the condition of anonymity.

Al-Zarqawi's whereabouts are unknown, but the Web site on which the tape appeared had a transcript heading that said al-Zarqawi was in Iraq. Breaking with his pattern of not claiming credit for attacks and not making taped public pronouncements, he took responsibility in the message for the attacks on the U.N. headquarters in Baghdad, the Jabal Lebanon Hotel in Baghdad and an Italian police station in Nasiriyah, among others.

The message reiterated themes from a letter U.S. authorities released in which al-Zarqawi purportedly wrote to other Al Qaeda leaders that the best way to undermine U.S. policy in Iraq was to turn the country's religious communities against each other. The letter was found on an Al Qaeda figure captured in northern Iraq in January.

A U.S. official, speaking on the condition of anonymity, said it isn't clear why al-Zarqawi released the tape, though he may have wanted to more fully explain his strategy.

The official said he also makes reference to history, quoting scholars, suggesting he is trying to appeal to a broader Sunni Muslim audience.

On the tape, al-Zarqawi said Shiite Iraqis were not true Muslims and were "the ears and the eyes of the Americans" in Iraq. He called upon Sunni Muslims in Iraq to "burn the earth under the occupiers' feet."