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BAGHDAD, Oct 27 (Reuters) - A battle between al Qaeda in Iraq and a major Sunni Arab insurgent group killed at least 16 militants on Friday near the ancient city of Samarra, a senior security officer told Reuters on Saturday.

The fighting involved the Islamic Army, a nationalist group that has been hostile to al Qaeda since June and has fought the Sunni Islamist group in areas of Baghdad and some Sunni towns.

A security source in Salahuddin province, speaking on condition of anonymity, said two non-Iraqi Arabs and an Iranian were among those killed in the battle.

"The clashes ended yesterday with militants from the Islamic Army taking control of the area," he said. The area had been controlled by al Qaeda for months.

"No Iraqi or U.S. forces intervened in the battle," he said.

Al Qaeda in Iraq has faced growing pressure from the Sunni Arab community, especially tribal leaders and home-grown insurgent groups who reject its hardline interpretation of Islam and its indiscriminate violence.

Signs of the group's weakening support were highlighted by an audiotape featuring Osama bin Laden, al Qaeda's overall leader, which aired on Monday.

Bin Laden conceded wrongs had been committed because of fanaticism in his group but urged Iraqi insurgent groups to unite with al Qaeda's Iraq wing.

Members of several insurgent groups have officially enrolled in "concerned citizen groups" fighting alongside U.S. and Iraqi troops to remove Sunni areas from al Qaeda control, especially in Diyala.

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