By Thomas Harding

The Daily Telegraph - The Army now believes that the Lynx helicopter shot down over central Basra at the weekend was most probably hit by a surface-to-air missile, obtained possibly from neighbouring Iran, after missile casings were discovered on the third floor of a nearby building, security sources in the city said yesterday.

The discovery, if confirmed, will be a worrying development for British operations in Iraq, which are increasingly reliant on helicopter "air bridges" to move men and equipment to reduce the risk of convoys being ambushed by roadside bombs.

The discarded missile parts were located when a search was conducted of the building as British troops swept the surrounding area.

A military observation post had also reported seeing an unusual level of activity in the building during the previous two days.

The missile is understood to have been identified as a Russian-made weapon that can be packed into a golf bag and quickly assembled and fired by one person with minimal training.

The Daily Telegraph has identified the type of missile but has been asked by the MoD not to reveal it on security grounds.

Hundreds of the missiles are known to have been sold to Iran and some to Syria, leading to speculation that some might have been passed to Iraq's insurgents.

If it is clear that the weapon is the sophisticated new missile then it will pose a threat to British and US aircrew in Iraq.

The MoD yesterday announced that a team of experts had been dispatched from Britain to Iraq to determine the exact cause of the crash. Their findings are not expected to be made public until autumn.