Two Americans also were killed in separate attacks Thursday and Friday in the northern city of Mosul, raising concerns that the insurgency was spreading north.
And in a blow to U.S. efforts to involve more foreign troops in securing Iraq, the Anatolia news agency reported that Turkey had decided no to send troops to Iraq.
Turkey's Parliament approved the deployment of peacekeepers in Iraq last month, but Iraqis have fiercely opposed having Turkish troops on their country's soil. The deployment may have involved as many as 10,000 troops.
It was not immediately clear whether the chopper was brought down by hostile fire or a mechanical failure, a spokeswoman said. But an officer who asked not to be identified felt a rocket-propelled grenade probably brought down the craft.
"Six soldiers were on board and all of them were killed," said Maj. Josslyn Aberle, a spokeswoman for the 4th Infantry Division based in Tikrit. They were all from the 101st Airborne Division, she said.
White smoke could be seen rising from the crash site on the east bank of the Tigris River as three other helicopters circled overhead. More helicopters could be seen hours later flying over a hilltop village on the west bank of the river.
In other developments:
In violence Friday, guerrillas attacked a convoy in the eastern part of Mosul, 250 miles north of Baghdad, with rocket-propelled grenades and small-arms fire Friday morning. The military said one U.S. soldier died and six others were wounded in the clash.
Three others were injured later in the day when a roadside bomb exploded near the Mosul Hotel, which is now used as a military barracks, the military said. A military statement released Friday said a soldier died the day before near Mosul when a homemade bomb exploded.
The latest confirmed U.S. military fatalities bring to at least 31 the number of American troops killed action in the first week of November. Two American civilian contractors working for the U.S. Army Corps of Engineers and a Polish officer also died in attacks over the past seven days.
The U.S. military said that the number of daily attacks on coalition forces dropped to 29 last week from a spike of 37 the week before.
The spate of attacks in the past week in Mosul, Iraq's third-largest city, has raised concerns among U.S. military commanders that the insurgency is spreading into that region from its main stronghold in the so-called Sunni Triangle, to the west and north of Baghdad.
The city is close to the semiautonomous Kurdish areas that lie between it and the Turkish border.