Baghdad, Iraq ? Tens of thousands of people have fled Samarra, about 60 miles north of Baghdad, in recent weeks, expecting a showdown between U.S. troops and heavily armed groups within the city.

Residents of the city said guerrillas told people to leave neighborhoods in anticipation of a larger battle after a clash on Tuesday in which U.S. warplanes bombed two houses, killing at least four people.

Samarra is now controlled by a volatile mix of tribes and gangs, some split along religious lines, and supporters of ousted President Saddam Hussein, according to interviews with numerous Samarra residents who have fled to Baghdad.

U.S. military authorities have been planning how to retake control of the city without a bloodbath. Officers said they are determined not to let Samarra follow what they call the Fallujah model. U.S. forces made an agreement to stay outside Fallujah, a city west of Baghdad, in order to end fierce clashes there during April. The city is now under the control of insurgents.

The U.S. military will try to mount a joint operation with Iraqi security forces, officials said. Under the plan, U.S. forces would likely seize Samarra in a powerful assault, and then have Iraqi National Guard or police patrol the city.