U.S. forces killed three civilians in this traditionally nationalistic northern Iraqi city today, a day after at least seven people were killed by the U.S. military during a riot in protest against the conduct of the American occupation.

The focus of the violence -- as it was Tuesday -- was central Mosul, where U.S. Marines and Special Operations soldiers have occupied the governor's offices. Looters ransacked the building five days ago after Iraqi forces abandoned the city.

According to witnesses, when suspected thieves tried to enter the Central Bank building around the corner, newly installed Iraqi police fired shots into the air to disperse them. U.S. guards atop the governor's building then shot toward the bank and killed three, by some accounts the would-be looters.

"Police fired at the looters. The Americans started firing," said a truck driver, Amal Yasser. "It's getting crazy around here."

Tuesday's protest, riot and subsequent killings seem to have been sparked by U.S. plans to administer the city through Mashaan Juburi, a former commander of deposed president Saddam Hussein's bodyguards as well as special Iraqi forces. In 1991, he led troops involved in putting down an uprising by Shiite Muslim rebels in southern Iraq. Some of the rioters carried photos of Shiite clerics.

Accounts of how the disorder began and why the U.S. forces opened fire differed widely. Abdul Rahman Hassan Ali, a baker who attended the demonstration, said: "People saw Mashaan enter the governor's office. They had heard he was to be the new governor. They were angry and started throwing stones and anything else they could find."

He and several other witnesses said some of the protesters were armed.

Brig. Gen. Vincent K. Brooks, briefing reporters at the Central Command regional headquarters in Doha, Qatar, said U.S. forces came under "aimed fire" and returned fire against some of the demonstrators. He estimated the number of dead at seven.

Mosul is proving to be one of the most volatile cities under U.S. occupation. It has long been a standard-bearer of pan-Arab nationalism. Only a day after U.S. troops entered Mosul, Iraqi flags sprang up on street after street. In the wake of looting that preceded the Americans' arrival here, residents quickly challenged the U.S. role in running Iraq.

At a minimum, the incidents suggest that the U.S. military here is ill-equipped to handle civil disorder. The heavily armed forces are wary of Hussein supporters as well as potential suicide attackers.

Lt. Col. Robert M. Waltemeyer, the U.S. officer in charge of Mosul, appears to be investing heavily in traditional clan leaders to help keep the peace. He met with several today at his Mosul airport headquarters and plans more such gatherings in coming days that will include civic leaders, U.S. officials said.

Juburi belongs to the Iraqi National Congress, an anti-Hussein group headed by a former banker, Ahmed Chalabi. Juburi is a newcomer to opposition politics, however. He went into exile in Damascus, Syria, during the 1990s, but had little or no contact with established Iraqi opposition groups. Last year, he showed up at the London conference organized by six major U.S.-endorsed opposition organizations and was included in a 65-member opposition council at the request of Massoud Barzani, head of the Kurdistan Democratic Party.

It is not clear whether the demonstrators were aware of the Kurdish connection. Moslawis, as residents here are known, are wary of an effort by Kurds, a minority in the city, to control Mosul's fate. In any event, many in Mosul seem to be suspicious of U.S. motives.

"We want to choose who runs our lives. We don't want old Saddam people to rule us," said Ahmed Qusay, a history teacher.

Iraqi men grieve over the bodies of their father and brother, who were killed during an incident involving U.S. forces in the northern Iraqi city of Mosul. Witnesses said the gunfire began when men tried to enter a bank near the governor's office.U.S. troops talk with Iraqi Arabs in central Mosul, where a riot that broke out on Tuesday left at least seven people dead. Accounts differed, but a U.S. military spokesman said American forces returned fire against some of the demonstrators.