The crack marksman used a semiautomatic Barret Light .50 calibre rifle to shoot the ISIS extrimists dead - despite them being behind a 10in thick brick wall.

The incredible incident happened during the battle for Ramadi in Iraq last week and the staff sergeant was part of a small team of British special forces who have been advising the Iraqi army.

A source told media: "The bodies of the ISIS fighters had been absolutely pulverised.

"One had been decapitated and another had been cut in half."

It is claimed the terrorists were in a building that was being used by ISIS thugs to coordinate suicide bomb attacks against the Iraqi army.

It is alleged that an airstrike had been considered but then turned down due to the possibility of too much collateral damage.

Rocket attacks were also turned down amid fears the building could collapse .

The SAS sniper then offered his services - which were gratefully accepted by the Iraqis.

He positioned himself in a building around one kilometre away and then fired some 30 armour-piercing rounds into the building - killing the trio of butchers and demolishing the wall.

The source claimed the action saved the lives of around 20 innocent civilians.

He added: "The suicide attacks had been stopped and, without any command and control, the ISIS fighters had retreated into another part of the city."

The rifle the staff sergeant used is thought to be the most powerful in the world and has a range of more than a mile as well as the ability to destroy aircraft and lightly-armoured vehicles, Mirror reported.

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