CAIRO, Egypt — Osama bin Laden’s chief deputy in an audiotape yesterday accused Shiite Iran of trying to discredit the Sunni Al Qaeda terror network by spreading the conspiracy theory that Israel was behind the terrorist attacks of September 11, 2001.

The comments reflected Al Qaeda’s no. 2 leader Ayman al-Zawahri’s increasing criticism of Iran.

Mr. Zawahri has accused Iran in recent messages of seeking to extend its power in the Middle East, particularly in Iraq and through its Hezbollah allies in Lebanon.

The authenticity of the two-hour audio recording posted on an Islamic Web site could not be independently confirmed. But the voice sounded like past audiotapes from the terror leader, and the posting where it was found bore the logo of Al-Sahab, Al Qaeda’s official press arm.

It was the second of two messages answering questions that were posted to Islamic militant Web sites earlier this year.

One of the questioners asked about the theory that has circulated in the Middle East and elsewhere that Israel was behind the 2001 attacks on the World Trade Center and the Pentagon.

Mr. Zawahri accused Hezbollah’s Al-Manar television of starting the rumor.

“The purpose of this lie is clear,” he said, to suggest “that there are no heroes among the Sunnis who can hurt America as no else did in history. Iranian media snapped up this lie and repeated it.”

“Iran’s aim here is also clear, to cover up its involvement with America in invading the homes of Muslims in Afghanistan and Iraq,” he said.

Iran cooperated with America in the 2001 U.S. assault on Afghanistan that toppled Al Qaeda’s allies, the Taliban.