A US military spokesman has said publicly for the first time that the four US helicopters shot down in Iraq in the past two weeks were shot down, confirming earlier witness reports and leaks from within the US military.

Twenty-one US soldiers and private security contractors were killed in the four separate incidents.

Major-General William Caldwell said: "There has been an ongoing effort to target our helicopters. We have had four helicopters shot down... It appears they were the result of some kind of ground fire."

He said the US was adjusting its use of helicopters while the incidents were investigated.

He said: "Based on what we've seen, we are already adjusting our tactics and procedures in how we deploy our helicopters."

The US military relies heavily on helicopters to transport its troops or launch air strikes against suspected fighters holed up in buildings.

Changing tactics

Dozens of US helicopters have come down, some of them hit by missiles or gunfire, in four years of fighting. But the unusually high number of helicopters lost in such a short time had raised questions about whether fighters had changed tactics or were using more sophisticated weapons.

A Black Hawk helicopter carrying 12 US soldiers and crew crashed northeast of Baghdad on January 20, amid suggestions that it had been brought down by a shoulder-fired missile.

Three days later, two helicopters flown by Blackwater security contractors were attacked while coming to the aid of US embassy personnel in central Baghdad.

One helicopter crashed under heavy gunfire, killing all four on board, while a fifth contractor was shot on the second helicopter, the US embassy said in a statement at the time.

An Apache was hit by machine-gun fire and its two crew killed while supporting Iraqi troops battling heavily armed followers of a messianic Muslim cult near Najaf last weekend.

In the latest incident, a helicopter crashed northwest of Baghdad on Friday, killing its two crew.

Photo caption

US Apache helicopters circles overheads as Iraqi forces and fighters clash in Ramadi