Usama bin Laden called for Iraqi insurgents to unite and avoid divisive "extremism," speaking in an audiotape aired Monday and apparently intended to win over Sunnis opposed to Al Qaeda's branch in Iraq.

In the audiotape broadcast on Al-Jazeera television, bin Laden said insurgents should admit "mistakes" and that he even advises himself not to be extreme in his leadership.

The tape appeared to be in response to moves by some Sunni Arab tribes in Iraq that have joined U.S. troops in fighting Al Qaeda members, as well as other Sunni insurgent groups that -- while still attacking Americans -- have formed coalitions opposed to Al Qaeda.

"Some of you have been lax in one duty, which is to unite your ranks," bin Laden said in the audiotape. "Beware of division ... Muslims are waiting for you to gather under a single banner to champion righteousness. Be keen to oblige with this duty."

"I advise myself, Muslims in general and brothers in al-Qaida everywhere to avoid extremism among men and groups," he said, saying leaders should not build themselves up as the sole authority, and that instead mujahedeen should follow "what God and his prophet have said."

Bin Laden used the Arabic word "ta'assub," which in traditional Islamic thought means extremism in allegiance or adherence to a group, to a degree that excludes others -- apparently advising flexibility to overcome divisions.

"Everybody can make a mistake, but the best of them are those who admit their mistakes," he said. "Mistakes have been made during holy wars but mujahedeen have to correct their mistakes."

U.S. counterterrorism authorities were studying the content and authenticity of the audiotape. However, officials often note that no one has faked a bin Laden recording in the past.

Al-Jazeera did not say how it obtained the tape.

IntelCenter, a a U.S. group that monitors militant messages, said it was bin Laden's third public statement this year, with the previous two on Sept. 8 and Sept. 20.