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LONDON — The identity of the masked executioner clutching a knife in ISIS beheading propaganda videos was revealed on Thursday.

A U.S. intelligence official confirmed to NBC News that a Londoner named Mohammed Emwazi is the person known as "Jihadi John" in the ISIS videos depicting the murders of American and British citizens. The militant's identity was first reported by The Washington Post, which cited "friends and others with familiar with his case." The BBC also named the individual without citing sources.

Emwazi is a Briton born in Kuwait who is known to intelligence services, according to the BBC and the Washington Post.

The Washington Post reported that Emwazi grew up in West London and graduated from college with a degree in computer programming before traveling to Syria in 2012 and joining ISIS.

The White House would not confirm or deny the identity, saying in a statement that the government continues to investigate the murder of American citizens by ISIS and that it does not comment on ongoing investigations. The Metropolitan Police said it would not confirm the reports and British government officials also declined to comment.

"Jihadi John" appeared in the videos showing the execution of American hostages James Foley and Steven Sotloff and Britons Alan Henning and David Haines.

He was given his nickname by the U.K. press because he was one of four Britons, dubbed the “Beatles” by their prisoners. He is also thought to have used the nom de guerre “Abu Saleh.”

Previously, British and American officials have said they believed they had ascertained his identity but not named any individual.

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Emwazi, who had strong links to Somalia according to U.K. security sources, appears to have become radicalized after he left university.

The International Centre for the Study of Radicalization, based at London’s King’s College, said it believed Emwazi’s identity “to be accurate and correct.”

A University of Westminster spokeswoman confirmed to NBC News that a student named Mohammed Emwazi left the college in 2009.

“If these allegations are true, we are shocked and sickened by the news,” she said in a statement. “With other universities in London, we are working to implement the government’s ‘Prevent’ strategy to tackle extremism.”

U.K.-based human rights group CAGE said it had worked with Emwazi in 2010 after he complained of being arrested and questioned by agents from Britain’s intelligence agency MI5 who accused him of links to Islamic extremism.

Emwazi told CAGE he had been detained in Tanzania in 2009 while attempting a post-college safari vacation with friends, and that he felt he had been harassed unfairly by intelligence agencies upon his return to Britain, the human-rights group said in a statement Thursday.

CAGE also released an email Thursday allegedly from Emwazi in which he complained that British authorities were unfairly preventing him from traveling to Kuwait.

“I have been trying to find out the reason for my refused Visa issue from my home country Kuwait, and a way to solve the issue,” the email from 2010 read. “So through my friends in Kuwait, it has been said to me that Kuwait has no problem with me entering, and the reason for my refusal is simply because the U.K. agents have told them to not let me in!”

He added: “Now I feel like a prisoner, only not in a cage, in London. A person imprisoned and controlled by security service men, stopping me from living my new life in my birthplace and my country, Kuwait."

CAGE research director Asim Qureshi said in the statement that Emwazi bore a “some striking similarities” to Jihadi John in the beheading videos but that there was “no way” he could conclusively identify him as the man behind the mask.

There was no answer at an address in west London where Emwazi was listed as living.

A British government spokeswoman told reporters: "We don't confirm or deny matters relating to intelligence. I am not going to get into the details of an ongoing police and security investigation."

IN-DEPTH

— Alastair Jamieson, Pete Williams, Alexander Smith and Sarah Burke