Baghdad, Iraq ? Two U.S. Army helicopters crashed in Baghdad on Saturday, killing two soldiers, as the military reported that four other American troops had died in car bombings elsewhere in Iraq. Insurgents also firebombed five Christian churches in the capital, causing damage but no injuries.

Military officials said they were investigating what caused the helicopters to crash Saturday evening in southwest Baghdad, the capital. Two other soldiers were wounded in the crashes.

The other American deaths came in two incidents in northern Iraq. A suicide car bomber struck a U.S. patrol near the town of Qaim along the Syrian border Friday, killing two soldiers, one Marine and an Iraqi translator, the U.S. military reported Saturday. Another soldier died of injuries suffered Friday in a car bombing near Mosul, about 220 miles north of the capital. Names of the deceased were withheld pending family notification.

In the “Sunni Triangle” city of Fallujah, west of Baghdad, many residents fled Saturday in anticipation of a U.S. military invasion after negotiations with city leaders broke down a day earlier. U.S. forces yielded control of the rebel focal point in April, and haven’t patrolled the city since. On Saturday night, American warplanes launched airstrikes against reported militant strongholds in Fallujah.

Iraqi Prime Minister Ayad Allawi has issued an ultimatum to Fallujahns to turn over Jordanian militant Abu Musab Zarqawi, believed to be responsible for a series of car bombings and beheadings in Iraq. U.S. forces suspect that Zarqawi is operating openly in the city.

U.S. forces and the Iraqi government are on a sustained military and political push to end parallel Sunni and Shiite-based rebellions and secure the country in advance of parliamentary elections scheduled for January. In both cases, the political approaches appear to be faltering.

In Baghdad’s Shiite bastion of Sadr City, militants from radical cleric Muqtada al-Sadr’s Mahdi Army continued to turn over weapons as part of a peace agreement to end weeks of violent clashes in the tightly packed slum.

The series of coordinated early-morning church attacks was the latest strike against the Christian minority in this predominantly Muslim country. On August, 11 people were killed when insurgents bombed five Christian churches in Baghdad and the northern city of Mosul.