Jihadis decapitated dozens of Yazidi women and dumped the heads in dustbins

British Special Forces made the grim discovery in Baghuz, eastern Syria

IS once controlled a swathe of territory more than a quarter the size of England

But by last night just 200 militants were confined to one-fifth of a square mile

Elite SAS troops found the severed heads of 50 sex slaves murdered by merciless Islamic State fighters as they led the assault on the terror group's last stronghold, The Mail on Sunday can reveal.

The barbaric jihadis had beheaded dozens of Yazidi women before dumping their heads in dustbins.

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British Special Forces made the grisly discovery when they entered Baghuz, the besieged town on the banks of the Euphrates in eastern Syria where IS is making its last desperate stand.

It followed a fierce close-quarter battle earlier this month during which SAS soldiers fired 600 mortar bombs and tens of thousands of machine-gun rounds, forcing the enemy into a network of tunnels beneath the rubble-strewn town.

More than 100 jihadis were killed during the battle. Two British soldiers were wounded, though neither has life-threatening injuries.

IS once controlled a swathe of territory more than a quarter the size of England but by last night just 200 militants were confined to one-fifth of a square mile

A source told The Mail on Sunday: 'In their hour of defeat, the jihadis' cruelty knew no bounds. They conducted a cowardly slaughter of these desperately unfortunate women as a final act of depravity and left their severed heads behind for us to find. The motivation for such a sickening act is beyond comprehension for any remotely normal human being.

'None of the SAS troops who entered Baghuz will forget what they saw, which some soldiers likened to a scene from the film Apocalypse Now. Their only solace is that they have contributed to bringing Islamic State's reign of terror to an end.'

The Mail on Sunday can today reveal extraordinary details of the role played by British forces on land and in the air to finally crush IS on the battlefield – and how some of the jihadis fled by disguising themselves as female refugees.

Five years ago, the terror group controlled 34,000 square miles of territory stretching from western Syria to eastern Iraq – equivalent to an area more than a quarter the size of England.

Fighters of the US-backed Syrian Democratic Forces (SDF) take a rest in the frontline Syrian village of Baghouz on February 19, 2019. - SDF forces have been fighting against the last shred of the Islamic State group's (IS) "caliphate" in eastern Syria.

Terrorist leaders proclaimed their new 'caliphate' and imposed their brutal rule on almost eight million people. They also generated billions of dollars from oil, extortion, robbery and kidnapping.

But by last night, a rump of 200 militants had been confined to one-fifth of a square mile of scrubland near Baghuz called Hawi al-Dandal, where they are understood to be holding an equal number of civilian hostages.

According to defence sources, SAS soldiers first deployed to Iraq and Syria in 2015, where they led an international manhunt for Mohammed Emwazi, the London-born militant known as 'Jihadi John' – he beheaded Western hostages and taunted international leaders with blood-curdling threats. Emwazi was killed by a precision air strike in Raqqa in November that year.

Vehicles belonging to the US-led coalition drive down a street in the frontline Syrian village of Baghuz, where the last IS fighters are holed up

Two years later, heavily armed SAS desert patrol vehicles were photographed at Al-Tanf on the Iraqi-Syria border. The Mail on Sunday understands that 65 troops from the elite regiment's B Squadron, accompanied by specialist mortar fire controllers and radio operators, left Al-Tanf to travel to Baghuz last month.

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They deployed in dune buggies and aboard Chinook helicopters from the RAF's top-secret Special Forces squadron. Artillery support for last week's final battle was provided by American and French Special Forces based at Al Qaim just over the Iraqi border. SAS operatives were also accompanied by hundreds of Western-trained troops from the Syrian Defence Force (SDF).

During the battle, RAF Typhoon fighter aircraft destroyed IS strongholds using Storm Shadow and Brimstone 2 rockets, while unmanned Reaper drones provided 24-hour surveillance coverage of Baghuz. An official defence source described as 'intense' the fighting as SAS and SDF troops targeted the strategically significant Baghuz-Bukhamal bridge during their advance on the town.

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A source said: 'The battle proper began on February 9. In the first two days, 37 IS fighters were killed and 19 enemy positions were destroyed, including the jihadis' operational control centre in a mosque in Baghuz on February 11.

'An advance by the SAS and SDF troops caused IS to go underground, utilising a network of tunnels under the town, but the rats couldn't escape because, even with the heavy cloud cover and dust storms, we were able to use drones effectively and identify openings to these tunnels.

'Co-ordinates for these positions were passed to SAS mortar teams and the US-French artillery units which pounded these positions.

'There was then a lull in the fighting while a humanitarian corridor was established, allowing around 1,500 civilians to be driven out of Baghuz in a column of 17 trucks.

A member of the Syrian Defence Forces stands guard on top of a building in the frontline Syrian village of Baghuz, on February 17

'Most of those leaving the town were women and children, but the convoy also included IS fighters disguised as women, who were taken into captivity.'

From February 12, SAS and SDF troops equipped with sophisticated night-vision equipment were inserted covertly into Baghuz, an agricultural town where 10,000 citizens have been terrorised by IS.

Sources said the team reported to commanders that many of the tunnels had been destroyed and that the jihadis had withdrawn.

In their place, however, the Islamists had left a treacherous web of landmines and rigged abandoned cars and homes with explosives.

A member loyal to the Islamic State waves its flag in Raqqa June 29, 2014. The group used to control vast swathes of territory in Syria and Iraq but has been cornered and is likely to be defeated 'in days'

As a result, specialist teams were called to dissemble the daisy chains of bombs, a painstaking process which took several days.

According to defence sources, a further 26 IS fighters were killed by the SAS and international forces in the Baghuz area on February 14.

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The following day, around 200 jihadis surrendered, with the dishevelled fighters searched by the SDF for hidden weapons.

Iris-recognition technology was used to identify high-ranking terrorists whose biometric data had previously been harvested by Special Forces.

The fighting continued last week, which is when The Mail on Sunday understands that SAS troops made the horrific discovery of the heads of the murdered Yazidi sex slaves. They also found the remains of IS fighters killed in the battle and jihadis assassinated by their commanders, apparently on suspicion that they were spies.

However, it is feared that more than 100 hardcore jihadis have successfully passed themselves off as refugees fleeing the fighting and they are now in camps set up to house and feed civilians displaced by the war.

Last night, the Ministry of Defence confirmed the role of RAF Typhoons in the Battle of Baghuz, but a spokesman declined to comment on the role of British Special Forces.