Notorious terrorist 'Jihadi John' may have been killed in drone strike
The UK has been working "hand in glove" with the US on tracking down the British IS militant known as Jihadi John, Downing Street said after he was targeted by a US air strike.
The Pentagon said it was assessing whether Mohammed Emwazi was killed by the operation in the militants' stronghold of Raqqa in Syria.
Prime Minister David Cameron is to make a statement later today.
"We have been working hand in glove with the Americans to defeat Isil and to hunt down those murdering hostages," a Number 10 spokeswoman said.
"The Prime Minister has said before that tracking down these brutal murderers was a top priority."
Emwazi came to notoriety in a video in August 2014 which showed the beheading of US journalist James Foley.
He also appeared in videos showing the killings of UK hostages Alan Henning and David Haines, American journalist Steven Sotloff, aid worker Abdul-Rahman Kassig and Japanese journalists Kenji Goto and Haruna Yukawa shortly before they were killed.
A US official told the Associated Press that a drone had been used to carry out the attack on a vehicle in Raqqa which was believed to be carrying Emwazi.
Pentagon press secretary Peter Cook said: "US forces conducted an air strike 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."
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 the 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 had 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 September, it was announced that two British nationals fighting with IS in Syria had been killed in an RAF drone strike.
Reyaad Khan, from Cardiff, who was said to present a "clear and present danger", was the target and died alongside fellow jihadi Ruhul Amin.
A third Briton, Junaid Hussain, who was said to be plotting with Khan, was killed three days later by a US drone.
The operation is being investigated by the Intelligence and Security Committee (ISC) which oversees the work of MI5, MI6 and GCHQ, after concerns were raised about its legal basis.