FIFTEEN US soldiers died and 21 were wounded yesterday when a Chinook helicopter was destroyed in a missile attack launched by Iraqi rebels west of Baghdad.

Defence Secretary Donald Rumsfeld described the attack as a national tragedy for the US and said that those responsible would be defeated.

He said: "It's clearly a tragic day for America. In a long, hard war, we're going to have tragic days.

"But they're necessary. They're part of a war that's difficult and complicated."

In a separate incident, the US command said a soldier from the 1st Armored Division was killed just after midnight yesterday when a bomb exploded near his vehicle.

The stricken helicopter was carrying dozens of soldiers to start leave abroad when it was struck by a missile and crashed in a cornfield.

Witnesses said they saw two missiles fired at the helicopter, which came down near the village of Hasai, six miles south of Fallujah, a centre of Sunni Muslim resistance to the US occupation.

The helicopter was with another Chinook carrying more than 50 passengers to the US base at the former Saddam International Airport, renamed Baghdad International Airport.

Witnesses said the second helicopter hovered over the downed craft for several minutes and then landed, apparently to extinguish a fire - but the downed helicopter had been destroyed.

At least six Black Hawk helicopters hovered over the area later, and dozens of soldiers swarmed over the site. The injured were still being evacuated at two hours later.

It was the deadliest day for US troops in the six-month-old occupation of Iraq, and the second-deadliest since the US-led invasion.

Mr Rumsfeld said the US had no hard evidence that ousted President Saddam Hussein was co-ordinating the attacks against troops

"The fact that he's not been captured or killed is important," Mr Rumsfeld told ABC's This Week.

"His regime was so vicious and did so many horrible things to people that people are frightened. They're frightened he could come back. He's not coming back, but until he's dead or captured, there is that concern."

Mr Rumsfeld blamed different elements for the surge in violence against the US occupation.

"We know why they're doing it," he said.

"There are criminals in that country who will do things for money. There are foreign terrorists in that country who have come back in from Iran and are trying to kill people. And there are the remnants of the Ba'athist regime.

"They want to take that country back, and they're not going to. They're not going to come close to taking that country back."

As of yesterday, 360 US service personnel have died since the beginning of military operations in Iraq, according to the Defence Department.

A total of 222 US soldiers have been killed on or since May 1, when Mr Bush declared that major combat operations had ended.