An SAS sniper is said to have shot dead an ISIS jihadi from 1.5miles away using the world's most powerful rifle.

It took three whole seconds for the bullet to reach its target - the throat of an Islamic State terrorist in the Iraqi city of Mosul.

The British marksman was using a CheyTac M200 Intervention gun which is produced in South Carolina and retails at $13,800 (£10,500) and can vaporise a person's organs from 2,500m.

A US soldier searches for an enemy sniper position during the invasion of Fallujah, Iraq (file photo)

An Iraqi soldier walks along a battered road in Mosul, Iraq, carrying a huge rocket launcher

The CheyTac M200 Intervention gun used by the SAS sniper which is widely regarded as the most powerful rifle in the world

As the terrorist was leaving a burned-out building two weeks ago, the SAS gunman is said to have pulled the trigger, registering one of the most difficult kills in the regiment's history.

Widely regarded as the most powerful rifle on the planet in its class, it has a working range of up to 3,000m and holds the record for the world's longest shot.

The soldiers is said to have only taken a single shot to take down his man, living up to the gun manufacturer CheyTac's motto of 'Make every shot count'.

A source told The Star on Sunday: 'It was a classic counter-sniper operation. The ISIS gunman was moving all the time to get into the best position to get a kill.

'It was like a game of cat-and-mouse and at one point the SAS almost gave up, believing that the terrorist had gone to ground.

'Just as the light was beginning to fade the gunman moved into what he thought was a safe location and lifted his rifle up into his shoulder before the SAS shot him dead.'

A member of Iraqi rapid response forces takes position during clashes with Islamic State fighters in western Mosul, Iraq on May 21, 2017

Smoke rises from an airstrike during a battle between Iraqi forces and Islamic State militants in western Mosul, Iraq, on May 21

The militant he killed was himself a sniper, using a Russian Dragunov gun and the British soldier had seen him gun down and wound several of his comrades.

His tactic would be to shoot, lay low for an hour, and open fire again.

It comes as the Iraq's special forces declared their mission in Mosul complete on Saturday after the group retook the last western districts from the Islamic State group within their area of operation, according to a military spokesman.

CheyTac M200 Intervention rifle The CheyTac M200 Intervention rifle is the sniper of choice used by the US Navy Seals, GROM operatives in Poland, Turkey's Maroon Berets and the Italian army. Costing $13,800 (£10,500), it is at the forefront of warfare weaponry. The British SAS are said to be trialing it in the field. It has been described as the most powerful rifle in the world with a range of 3,000m and can hit a person at 2,500m with enough power to vaporise their organs. A built-in a computer makes calculations to tell the shooter where to aim having factored in humidity, heat and wind. As a result it consistently achieves groups of 7 to 9 inches (18 to 23 cm) at 1,000 yards (914 m), 10 inches (25 cm) at 1500 yards (1372 m) and 15 inches (38 cm) at 2,000 yards (1,829 m). Advertisement

The announcement came despite ongoing battles in a handful of western Mosul neighbourhoods that continue to force hundreds of civilians to flee each day.

ISIS still controls some areas of western Mosul, including the dense Old City where some of the toughest battles are expected to play out.

Special forces spokesman Sabah al-Numan said his troops had completed their initial mission, but stood ready 'to support any other forces if we are ordered to by the prime minister'.

Elsewhere in central and southern Iraq, a series of bombings killed at least 27 people.

A suicide bombing Saturday near the oil-rich city of Basra killed at least eight people and wounded 41 others, according to a military commander.

Five civilians and three troops were killed when the bomber blew up his explosives-laden car on Friday at a checkpoint north of Basra just behind a bus waiting to be cleared, said chief of the Basra Operations Command, Lieutenant General Jamil al-Shimmari.

A second attacker drove down a desert road after the explosion and security forces killed him, Lt Gen al-Shimmari added.

In an online statement, IS claimed responsibility for the attack, saying it targeted Shiites.

Basra, about 340 miles south east of Baghdad, is home to about 70% of the country's proven oil reserves of 153.1 billion barrels.

Located on the Persian Gulf and bordering Kuwait and Iran, the city is also Iraq's only outlet to the sea and the hub for most of the country's oil exports, with 3.23 million barrels exported from Basra last month.

Cars destroyed in clashes are seen on a street during a battle between Iraqi forces and Islamic State militants in western Mosul, Iraq

ISIS also claimed responsibility for the double suicide bombings in Baghdad overnight that killed at least 19 people and wounded 33, according to an online statement.

Iraqi forces, backed by the US-led coalition, officially launched the operation to retake Mosul in October and the city's east was declared 'fully liberated' in January.

The fight for Mosul's west was launched the following month and has been marked by some of the most gruelling and deadly combat in the fight against IS in Iraq to date.