The battle began on Saturday night when two truckloads of gunmen opened fire on a US position near Donkey Island on the Euphrates River in the restive western province of Anbar.

US forces returned fire and, supported with aircraft, pursued the gunmen into the night.

"Helicopters killed at least one insurgent and wounded another, and destroyed the two trucks, later determined to be loaded with weapons, ammunition and explosives," a military statement said.

Insurgents shot down a US military helicopter south of Baghdad but its pilots escaped with only mild injuries, the military reported Tuesday.

"An AH-64 Apache helicopter rescued two Task Force Marne pilots after enemy fire brought down their O5-58D Kiowa Attack Helicopter south of Baghdad" on Monday, the military said.

The downed helicopter was later destroyed with two 500-pound (227 kilograms) laser-guided bombs, the military said.

At the height of the battle an Apache attack helicopter was ordered to evacuate a critically wounded soldier, a separate statement said.

A co-pilot "helped load the injured soldier into the front seat without further injury," it said.

"Despite the heavy small arms fire and surface-to-air fire events in the area, the co-pilot/gunner strapped himself on to the left side of the aircraft and hunkered down on the wing" outside the narrow fuselage.

The soldier was flown to a nearby US base -- in what a US marines spokesman described as "an amazing act of heroism" -- and is now in stable condition, the statement said.

Troops searching the area on Sunday morning discovered 22 dead insurgents, including seven wearing suicide vests, as well as 24 homemade grenades, 20 roadside bombs, and other weapons.

"Most of the enemy were dressed in similar white dishdashas (ankle-length shirts) and white running shoes, an outfit often associated with extremist fighters prepared to kill themselves," the statement said.

Clashes erupted again on Sunday afternoon, when insurgents attacked US-led forces with machine gun fire, grenades and a suicide vest.

Another insurgent was killed and two were detained in the ensuing battle as helicopters and fighter jets were scrambled to destroy an alleged bunker with precision-guided bombs.

The security situation in Anbar, once the epicentre of the country's Sunni insurgency, has been improving in recent months as local tribes have joined with US and Iraqi forces to fight al-Qaeda in Iraq.

al-Qaeda has responded by broadening its attacks to include the tribes as well as US and Iraq forces, and the province remains a dangerous area.

Ahead of Saturday's battle US-led forces had "received reports that a significant number of anti-Iraqi forces had gathered on the outskirts of Ramadi to stage a series of large scale attacks," the statement said.

In October last year al-Qaeda declared Ramadi to be the capital of an "Islamic State of Iraq", but since then it has seen its support collapse among the local population as tribal chiefs switch allegiances.

Now, the city itself is largely in the hands of US-alled Iraqi tribal and government forces, although commanders remain wary of a counterattack.