Large explosions rocked Baghdad on Friday night, as US forces targeted insurgents in the Iraqi capital.
The US has stepped up its offensive against rebels
Artillery rounds and heavy machine gun bursts reverberated around the city, as fighter aircraft opened fire overhead.
Earlier, a US army helicopter was shot down near Falluja, west of Baghdad, killing a soldier and injuring another.
As US military spokesman said the coalition was "fairly convinced" the OH-58 Delta Kiowa Warrior helicopter was brought down "by enemy fire".
The US military said the two-crew helicopter crashed on the open ground near a main road, 50 kilometres (30 miles) from Baghdad.
"The downed helicopter's wingman provided over-watch as paratroopers operating in the area secured the site," a statement from Central Command said.
Witnesses in Falluja said the helicopter came under fire and than crashed.
"We were in a joint patrol with US troops to remove landmines and I saw a helicopter hovering in the sky which was hit by a missile," said Iraqi policeman Mohammad Abdul Aziz.
"It was split into two and went down in flames."
Insurgents have recently shot down several US helicopters in the Falluja area, where support for ousted Iraqi leader Saddam Hussein remains strong.
In Baghdad, US forces continued their offensive - known as Operation Iron Grip - against Iraqi fighters in the city.
The BBC's Chris Hogg in Baghdad says the dull thud of artillery shells could be heard across rooftops accompanied by rapid fire from US military aircraft.
He says there were three attacks in the space of an hour, each lasting about 10 minutes.
Our correspondent says the last time the Americans launched raids on this scale was over Christmas, when for three days their gunners fired on areas of open ground south of Baghdad.
US forces have arrested more than 180 suspected guerrillas in Baghdad since Operation Iron Grip was launched in late December.