Osama bin Laden urged insurgent groups in Iraq to unite, saying divisions only helped the enemy, in an audio recording aired by Al Jazeera television this evening.
"The interest of the Islamic nation surpasses that of a group ... the interest of the (Islamic) nation is more important than that of a state," said a voice which sounded like the al Qaeda leader's.
"The strength of faith is in the strength of the bond between Muslims and not that of a tribe, nationalism or an organisation.
"I advise ... our brothers, particularly those in al Qaeda wherever they may be, to avoid fanatically following a person or a group," he said.
Al Jazeera said the tape was entitled "message to the people of Iraq". It was not clear from the part of the tape aired when it had been recorded.
Bin Laden said he was addressing "mujahideen (holy warriors) in Iraq", Sunni Muslim militant groups fighting US-led forces. Al Qaeda belongs to a school of Islam which regards members of Iraq's Shia majority as heretics.
Al Jazeera said bin Laden urged Iraqi tribes to uphold their "tradition of resisting" occupation, in an apparent reference to the presence of British forces in Iraq in the last century.
The speaker warned insurgents against enemy attempts to drive wedges between groups by planting agents among them, and said such agents should be punished, but only after their guilt was established through thorough investigations.
Iraq's wing of al Qaeda is one of the key groups fighting US-led forces and the Baghdad government. Bin Laden's followers have angered other Sunni groups and tribes through their hardline interpretations of Islam and indiscriminate killing of civilians.
Some Sunni groups have joined forces with al Qaeda to set up what they call an Islamic State in Iraq, but other groups and tribal leaders have rejected the move.
Last month, bin Laden issued three messages, including a video marking al Qaeda's September 11th, 2001, attacks on New York and Washington in which about 3,000 people were killed.
Bin Laden said in the video that United States was vulnerable despite its power and insisted only conversion to Islam would end the conflict.