THE shocking toll of six American helicopters shot down in Iraq within three weeks has sparked a Pentagon inquiry into the use of surface-to-air (Sam) missiles against the aircraft.

“Is there a concern? Yes, there is definitely a concern,” said a Pentagon official about the helicopter downings. “Are we looking at it closely? You bet.” Air power is crucial to American military strategy in Iraq — roads have become too dangerous to travel along because of roadside bombs that can penetrate even the armour of a US Abrams battle tank.

The shooting down of six helicopters with the loss of 27 lives is an unprecedented success for the Iraqi insurgency, and coincides with the “surge” operation of increased American troops in Baghdad backed up by Iraqi police and army.

The latest security clampdown follows two unsuccessful operations, Operation Together Forward I and Operation Together Forward II, both aimed at retaking Baghdad neighbourhoods. The previous operations failed when American troops pulled out and turned over the areas to Iraqi troops. Insurgents simply hid their weapons and returned when the Americans left.

Yesterday, Iraqi security forces found 50 Russian-made Sam missiles in a weapons cache near Baghdad. The discovery, the largest of its kind since 2003, has confirmed suspicions that insurgents are using more sophisticated munitions.

The Pentagon has confirmed that a CH46 Sea Knight shot down 11 days ago in Al-Anbar province west of Baghdad, the heartland of the Sunni insurgency, was the victim of a Soviet-designed Sam.

They had earlier claimed it had crashed because of mechanical failure. Sea Knights are troop transport vehicles, highly identifiable because of their huge size and twin rotors. They can carry up to 24 troops, with four crew.

British, American and Iraqi sources said the missile used was a version of the “Strela” series — a Sam designed in Russia and copied by countries as diverse as North Korea and Egypt.

Investigators are focusing on which version of the Strela was used. The Sam 7 (Strela 2) is cheap, available in Iraq on the black market for £500, and easy to use. One source said yesterday: “I could teach you to use it in one day. You just wait for the green light and the growling noise, and pull the trigger.”

The Sea Knight is more likely to have been shot down by the advanced Strela 3, or Sam 14, that locks on to the target more efficiently, but in Iraq they would cost up to £25,000 and would be used only by specially trained insurgents.

The Pentagon is concerned that the insurgents may also have access to the next-generation missile, the Igla, which can cost hundreds of thousands of pounds and is highly accurate.

It is a sensitive issue for the US military. While the Bush administration is pointing the finger at Iran for supplying weapons to Iraqi rebels, the Iranians are unlikely to be behind these helicopter attacks.

Most of the Shi’ite attacks are sectarian, on their Sunni enemies, while all the attacks on American helicopters have come from Sunni areas. The missile technology is believed to have fallen into the hands of former Saddam supporters or their Al-Qaeda allies.

On Sunni websites the insurgents have issued communiqués from the “air defence unit of the Islamic State of Iraq” taking responsibility for shooting down the American helicopters.

Muwaffaq al-Rubaie, the Iraqi national security minister, said yesterday in Baghdad: “Not all the American helicopters were brought down by missiles, some were lucky shots from ground fire such as heavy calibre machineguns. But the operation now going on is dependent upon both the military and their contractors flying on helicopters and there is evidence the insurgents are using missiles against them.”

The Pentagon source concurred. “Of the six helicopters that recently crashed, one flew into a telephone wire, one crashed because of unknown causes and the other four came down under fire from the ground. The last confirmed missile hit is the most worrying.” The new surge operation depends on helicopters to transport cargo, weapons and soldiers.

Times Recommends

• Mandela’s tribe threatens President Jacob Zuma
• The French empire strikes back
• Wife of cheating governor exacts a political revenge