CAIRO - Al Qaeda's No. 2 leader issued an audiotape yesterday accusing Iran of trying to discredit the power of the terrorist network by spreading a conspiracy theory about who carried out the Sept. 11 attacks.

Ayman al-Zawahri, Osama bin Laden's deputy, has boosted his denunciations of Shi'ite Iran in part to depict Sunni Al Qaeda as the Arabs' top defense against the Persian nation's rising power in the Middle East.

The increasing enmity toward Iran is a notable change of rhetoric from Zawahri, who had previously rarely mentioned the country - apparently in hopes he would be able to forge some sort of understanding with Tehran based on their common rivalry with the United States. Iran has long sought to distance itself from Al Qaeda.

"Al-Zawahri wanted to work with Iran, but he's deeply disappointed that Iran has not cooperated with Al Qaeda," said Rohan Gunaratna, a terrorism analyst and author of "Inside Al Qaeda: The Global Network of Terror."

Now Zawahri "wants to appeal to the anti-Shi'ite, anti-Iran sentiments in the Arab and Muslim world," said Gunaratna, head of the International Center for Political Violence and Terrorism Research in Singapore.

Zawahri appeared intent on exploiting widespread worry in the Arab world over Iran's influence, particularly in Iraq. He also sought to denigrate Iran's ally Hezbollah, which has gained some popularity even among Sunnis in the region for its fight against Israel.

Zawahri's comments came in a two-hour audio posted on an Islamic militant website, the second message in weeks in which he answered hundreds of questions sent to the site by Al Qaeda sympathizers and others.

The question-and-answer campaign is a sign of the terrorist group's sophistication in its use of the Web. It shows Al Qaeda can post frequent messages from its leaders while keeping in touch with its base - even though the leaders are in hiding, presumably on the Afghan-Pakistan frontier.

The Web is a key tool of Al Qaeda's central leadership to inspire and direct sympathizers, although some terrorism analysts question how much control they have over Islamic militants. Al Qaeda branches in Iraq and Afghanistan are believed to have close ties with the network's core, but little is known about its level of control elsewhere.

The authenticity of the audio could not be independently confirmed. But the voice sounded like past audios from Zawahri.

Zawahri spoke on a wide range of topics in yesterday's message. He told a female questioner there were no women in the ranks of Al Qaeda but praised wives of mujahideen for their "heroic role in taking care of their homes and children amid the trials of exile." Female suicide bombers have carried out attacks in Iraq, some of them believed to be by Al Qaeda's branch in the country. Zawahri appeared to mean no women were among the network's core leadership.

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