The world's most wanted man, Jihadi John, is believed to have been killed in a US drone strike inSyria.
Pentagon officials say they are '99 per cent' sure they have assassinated British Islamic State executioner Mohammed Emwazi in the terror group's capital of Raqqa.
The 27-year-old from London, who became the face of ISIS in their sickening beheading videos of Western hostages including two British aid workers, was 'evaporated' by a missile as he climbed into a vehicle.
A senior US defence official told Fox News: 'We are 99 per cent sure we got him. We were on him for some time.'
The Kuwaiti-born militant, who moved to the UK when he was six years old, was blown up in a 'flawless' and 'clean hit', another defence source told ABC News.
However, there is a good chance his death will never be confirmed if his body has been incinerated and spies may have to rely on intercepting chatter from the jihadi militants to verify the reports.
Emwazi has been the subject of an international manhunt for more than a year after he first appeared in a barbaric execution video in August last year.
He was top of the UK Government's 'kill list' of up to a dozen radicals who ministers want killed in drone strikes and Downing Street today said Britain had been working 'hand in glove' with the U.S. to track him down.
There is a high possibility British spies would have been operating on the ground in Raqqa to help identify Emwazi before the strike.
Prime Minister David Cameron is due to give a statement on reports of his death later today.
A Number 10 spokeswoman said: 'We have been working hand in glove with the Americans to defeat Isil (ISIS) and to hunt down those murdering hostages.
'The Prime Minister has said before that tracking down these brutal murderers was a top priority.'
A senior U.S. official, quoted by CNN, said the drone strike came after 'persistent surveillance' and claimed the authorities were certain it was Emwazi when they fired the missile.
The drone is believed to have been tracking Emwazi for most of the day yesterday and he was 'ID'd and engaged' when he came out of a building and got into a vehicle in Raqqa.
Another senior military source told the BBC there is a 'high degree of certainty' he had been killed.
Anti-ISIS activist group Raqqa Is Being Slaughtered Silently (RIBSS), which operates in the Syrian city, reported that Emwazi was killed at around 11.40pm last night and said it counted 14 air strikes in just nine minutes between 11.51pm and midnight.
The Syrian Observatory for Human Rights, a Britain-based monitoring group, said four people were killed in the strike late on Thursday.
'The car was hit in the centre of town, near the municipality building,' Observatory chief Rami Abdel Rahman said.
He said sources described one of those killed as a 'senior British member of the group'.
The strike is also understood to have hit another member of 'The Beatles' – a nickname given to three British-sounding ISIS captors who guarded Western hostages, with Jihadi John being a reference to John Lennon.
A second member of the cell – nicknamed 'Jihadi George' after George Harrison – is believed to be London rapper Abdel-Majed Abdel Bary who fled to Syria in 2013.
The former rap star, whose father was a key lieutenant of Osama bin Laden, was among the first foreign fighters to take up arms in the warzone two years ago.
However, it was reported in July that he had fled to Turkey after becoming disillusioned with jihadi life.
Confirming the drone strike late last night, Pentagon Press secretary Peter Cook said: 'US forces conducted an airstrike in Raqqa, Syria, on November 12, 2015 targeting Mohamed Emwazi, also known as Jihadi John.
'We are assessing the results of tonight's operation and will provide additional information as and where appropriate.'
He was involved in the murders of British aid workers David Haines and Alan Henning, American journalists Steven Sotloff and James Foley, American aid worker Abdul-Rahman Kassig (also known as Peter Kassig) and Japanese journalist Kenji Goto.
Mr Haines, an aid worker from Scotland, was executed in September last year, having been held captive for 18 months.
His daughter Bethany later said she felt families of Emwazi's victims would only feel closure 'once there's a bullet between (his) eyes'.
A video released a month later showed 47-year-old Salford taxi driver Mr Henning appearing to be beheaded.
His daughter Lucy said she found out he had been killed when she saw an image posted on social media site Instagram.
Emwazi appeared in the videos dressed in black with only his eves visible, and spoke with a British accent as he went on anti-western rants to the camera while wielding a knife.
It was not until February this year that the jihadist was unmasked as Kuwaiti-born Emwazi, who lived in the UK since the age of six.
It emerged that Emwazi had been known to British intelligence services, but managed to travel to Syria in 2013.
In the videos, the tall masked figure was clad in black and speaking in a British accent.
He began one of the gruesome videos with a political rant and a kneeling hostage before him, then ended it holding a large knife in his hand with the headless victim lying before him in the sand.
Journalist Sotloff's mother, Shirley Sotloff was unaware of the air strikes, but said Emwazi's death would not bring closure.
She told NBC News: 'If they got him great. But it doesn't bring my son back.'
Diane Foley, the mother of James Foley, who previously said she had forgiven Emwazi, told ABC News: 'This huge effort to go after the this deranged man filled with hate when they can't make half that effort to save the hostages while these young Americans were still alive.'