BAGHDAD -- A U.S. military boat patrolling the Tigris River at night drew fire yesterday from Iraqi security forces who mistook it for the enemy, sparking a deadly gun battle that killed seven Iraqis and drew local anger over U.S. use of firepower against friendly forces.

Iraqi officials said three soldiers, two police officers and two paramilitary fighters known as Sons of Iraq and allied with U.S. and Iraqi forces were killed in the clash in Tarmiya.

The U.S. military confirmed only "an incident involving weapons fire," and said reports indicated that Iraqi security forces had sustained casualties. "It is always regrettable when incidents of mistaken fire occur," it said in a brief statement, adding that a review of the incident was under way.

A police officer in Tarmiya, 37 miles north of Baghdad, said the U.S. boat was moving without its lights on, raising suspicions among Iraqis at a fixed checkpoint on a bridge spanning the river.

The area is known for Sunni Muslim insurgent activity. On Monday, a teenage suicide bomber tried to kill a Tarmiya city official whose father is a tribal leader and a chief backer of the local Sons of Iraq. The target of the assassination attempt, Emad Jassim, was critically injured.

Yesterday's deaths were likely to rev up debate among Iraq's leaders about the issue of immunity for U.S. forces in this country. The immunity question has figured prominently in negotiations between the United States and Iraq over a deal that would allow U.S. troops to stay in Iraq after this year. The Iraqis are proposing the Americans retain immunity on their bases and on combat missions authorized by the Iraqi government. But they would be brought before an Iraqi court in other circumstances, according to Iraqi officials.

An Iraqi army member in Tarmiya said it was "unbelievable" that the Americans would not have known that there was an Iraqi security force checkpoint at the bridge, which sits at a strategic location.

There have been several Sons of Iraqi fighters killed by U.S. forces in the past year, frequently because they are mistaken for insurgents while out on missions or at checkpoints. The U.S. military says the Sons of Iraq would be secure if they did not stray from their assigned checkpoints, and if they wore the reflective vests identifying them as friendly forces. But in the field, there are no communications between U.S. patrols and their Iraqi counterparts, and most mistaken shootings occur at night.