Insurgents downed Iraq helicopter

There has been a sudden upsurge in helicopters being shot down

A US helicopter which crashed in Iraq last week killing all seven marines aboard was shot down, US officials say.

At the time of the crash in north-west Baghdad military officials said they believed the CH-46 had suffered mechanical failure.

But US spokesman Major Jeff Pool said further investigations had now confirmed the cause to be hostile fire.

It is the fifth time a US military helicopter has been shot down in Iraq in less than three weeks.

In the wake of the attack on the twin rotor CH-46 Sea Knight helicopter a video appeared on the internet, allegedly posted by al-Qaeda in Iraq, which seemed to show the aircraft being hit by a ground-to-air missile.

Two civilian helicopters have also been shot down in recent weeks.

Tactical questions

The BBC's Jane Peel in Baghdad says that the sudden upsurge in deadly attacks on helicopters is of huge concern to the US military, who say that they are dealing with a "thinking enemy".

The recent incidents have raised new questions about whether insurgents are using more sophisticated weapons, and whether US tactics need changing, correspondents say.

However, Maj Pool refused to go into detail about the new threat:

"Because of the sensitive operational nature of the recent events, speculation as to capabilities of the enemy's weapons, or our tactics to counter them, will not be discussed to guard the safety of our service members," he said.