The Pentagon has announced the loss of an Apache combat helicopter over western Iraq, saying it was apparently downed by hostile fire.
Helicopters constantly back up ground operations in Iraq
An F-16 warplane also crashed south-west of Baghdad with the cause of the accident still under investigation.
The two-member crew of the helicopter and the F-16's pilot were not injured and were rescued by coalition forces, US Central Command reported.
American forces carried out raids targeting elements loyal to Saddam Hussein's ousted regime on Thursday while reports have been coming in of violent clashes in the northern city of Mosul.
Unconfirmed reports say a number of people may have been killed or wounded as hundreds of Iraqi ex-soldiers demanding their army pay clashed with police guarding Mosul's administrative buildings.
Witnesses who spoke to AFP news agency said that US helicopters circled above the city as the soldiers traded fire with the police.
The unrest apparently erupted after the local government began paying April salaries to civil servants but refused to pay ex-members of the Iraqi forces.
On the loss of its helicopter west of Baghdad, the Pentagon said two other Apaches had engaged "irregular forces" in the crash area.
They said the F-16 crashed at 0630 local time (0230 GMT).
"The cause of the incident is unknown at this time and will be investigated," Central Command said.
Elsewhere in Iraq, American planes carried out air strikes as part of what they say is a continuing campaign to eradicate Baath party loyalists.
US officials said the warplanes hit a "terrorist" training camp 150 kilometres (93 miles) north-west of Baghdad, and this was followed by fighting on the ground in which one member of the US-led forces is reported to have been wounded.
US troops are still working to restore order
The fighting is part of the biggest US military operation in Iraq since the end of the war.
Thousands of soldiers, including air assault teams, river patrol boats and Iraqi police officers, are taking part in the raids.
So far 400 suspects have been rounded up.
US intelligence believes suspects have found refuge in several communities on a peninsula along the Tigris River, north-east of the town of Balad, 70 kilometres (45 miles) from Baghdad.
Early on Monday, US forces moved into position on the edge of the peninsula and established multiple checkpoints, cutting off escape routes to suspected militants.
Nearly 30 US troops have died in fighting or accidents since 1 May, when President Bush declared the war in Iraq effectively over:
There were 85 attacks on US forces in May alone - almost triple the number of the previous month
On Tuesday a US paratrooper was killed and another injured in a grenade attack in Baghdad
Before that, another US soldier was killed by gunmen after they reportedly approached a checkpoint and asked for medical help