The crippled Chinook helicopter came down in farmland at 9:00am (1:00am EST) near the village of Baisa, south of Falluja, a fiercely anti-U.S. town 30 miles west of the capital.

US helicopters circled above the smoking wreckage. Other helicopters and US Humvee vehicles were parked nearby.

US Army spokesman Colonel William Darley told reporters that the cause of the crash was under investigation.

Witnesses said the helicopter, carrying troops on a rest and recreation break, had been shot down by Saddam remnants.

Some Iraqis were jubilant. "The Americans are pigs. We will hold a celebration because this helicopter went down -- a big celebration," said wheat farmer Saadoun Jaralla near the crash site. "The Americans are enemies of mankind."

It was the third time a US helicopter was brought down since US President George W Bush declared major combat over in Iraq on May 1. The Americans invaded in March.

"Clearly it is a tragic day for Americans," Defence Secretary Donald Rumsfeld told ABC television. "In a long hard war we are going to have tragic days."

But he said the United States would not be deterred and would win the war in Iraq.

Bush vowed on Saturday to stand firm and said leaving Iraq prematurely would strengthen the "terrorists" he said were to blame for recent deadly suicide attacks.

A U.S. spokesman said two Chinooks had been heading for Baghdad airport when one was "shot down by an unknown weapon."

A witness in Falluja, Dawoud Suleiman, said: "There were two American helicopters. They fired a missile at one and missed, and then they hit the other, which crashed and caught fire."

Before the helicopter attack, 123 U.S. soldiers had died in hostilities in Iraq in the past six months, including one killed by an overnight roadside bomb blast in Baghdad and two killed by a bomb in the northern city of Mosul the day before.

UPSURGE IN VIOLENCE

Rocket and bomb attacks have killed 12 U.S. soldiers in an eight-day upsurge in violence that began when guerrillas rocketed a Baghdad hotel where U.S. Deputy Defence Secretary Paul Wolfowitz was staying last Sunday.

The next day four suicide attacks killed 35 people at the offices of the International Committee of the Red Cross and three police stations.

The attacks prompted the United Nations, the ICRC and other aid agencies to pull more foreign staff from Baghdad and review their operations, in a fresh blow to reconstruction efforts, although the U.S. military commander in Iraq plays them down.

"The coalition has maintained its offensive focus in the face of what we regard as a strategically and operationally insignificant surge of attacks," Lieutenant-General Ricardo Sanchez told a news briefing on Saturday.

In Falluja, residents said a roadside bomb had hit a convoy of U.S. personnel in civilian vehicles. At least one vehicle was ablaze at the scene, where gloating crowds shouted anti-U.S. slogans. Television pictures showed a gleeful youth wearing a U.S. Army helmet. Others danced on wreckage.

In Baquba, northeast of Baghdad, residents said a roadside bomb had exploded as a U.S. convoy passed, hitting a bus carrying university students and wounding two women.

Iraq's six neighbors plus Egypt held security talks in Damascus, mindful of U.S. assertions that Syria and Iran were not doing enough to prevent militants crossing into Iraq.

In a statement, they condemned "terrorist" attacks on "civilians, humanitarian and religious institutions, embassies and international organizations" and vowed to cooperate with Iraqi authorities to "prevent any violation of borders."

Iraq's interim foreign minister, Hoshiyar Zebari, had turned down a belated invitation to attend. Officials at his ministry said Syria had been loath to ask him because of misgivings about being seen to recognize Iraq's U.S.-backed interim government.

U.S. troops and Iraqi police had tightened security in Baghdad and other cities over the weekend in response to rumors that guerrillas planned another series of bombings.

Many fearful parents kept their children out of schools for a second day. The deputy headmistress of the Baghdad Middle School for Girls said only a fifth of 750 pupils had turned up.

"They're staying away because they're afraid of explosions. We've tried to assure parents that it's safe," she said.