'Jihadi John' Reported Dead Following US Airstrikes in Raqqa

US forces believe they have killed the British Islamic State militant known as "Jihadi John" in airstrikes in the northern Syrian town of Raqqa, it was announced Thursday.

The Pentagon confirmed it had carried out airstrikes targeting British citizen Mohammed Emwazi — known for appearing in a string of horrific IS beheading videos — and was still assessing their effectiveness. The British government told the Guardian it had worked "hand in glove" with the US to coordinate the strikes, with sources adding there was "high degree of certainty that [Emwazi] has been killed."

A senior US defence official told Fox News: "We are 99 percent sure we got [Emwazi]. We were on him for some time." A US military source said there was a "high degree of certainty" he had been killed, reported the BBC.

British Prime Minister David Cameron said he could not yet be certain Emwazi had been killed.

Speaking outside 10 Downing Street, Cameron said: "We've been working with the United States literally around the clock to track him down… He was ISIL's lead executioner. This was an act of self defense. It was the right thing to do."

He added: "[Emwazi] posed an ongoing and serious threat to innocent civilians, not only in Syria but in the UK and around the world too.

"Let us not forgot that he killed many, many Muslims too. Today I want to thank the United States. The UK has no better friend."

Related: Islamic State 'Defeated and On the Run' From Sinjar

The monitoring group the Syrian Observatory for Human Rights (SOHR) said a leading British IS member three other foreign militants were killed in the bombings.

"A car carrying four foreign Islamic State leaders, including one British Jihadi was hit by US air strikes right after the governorate building in Raqqa city," SOHR director Rami Abdulrahman told Reuters.

"All the sources there are saying that the body of an important British Jihadi is lying in the hospital of Raqqa. All the sources are saying it is of Jihadi John but I cannot confirm it personally."

If Emwazi's death is confirmed, it would be an important milestone in the US-led campaign against the group and would come more than a year after US President Barack Obama promised justice after the deaths of American hostages.

Dressed entirely in black, a balaclava covering all but his eyes and the bridge of his nose, Jihadi John became a menacing symbol of IS brutality and one of the world's most wanted men.

The videos showed the killings of US journalists James Foley and Steven Sotloff, US aid worker Peter Kassig, British aid workers David Haines and Alan Henning, Japanese journalist Kenji Goto, and other hostages.

As the families received news of the strike, Alan Henning's nephew Stuart tweeted that he had "mixed feelings" as he had wanted Emwazi to suffer "the way Alan and his friends did."

Related: Islamic State's 'Jihadi John' Named as Mohammed Emwazi from West London

Mixed feelings today wanted the coward behind the mask to suffer the way Alan and his friends did but also glad it's been destroyed ????

— Stuart henning (@Skyblublood)November 13, 2015

Henning's brother Reg said: "Hopefully this is the end of it. I am glad he is dead.

"I would have preferred him to face justice. I think things will quieten down. If they had arrested him and gone to court, it would have dragged on for months and months."

Bethany Haines, daughter of David Haines, said in a statement: "After seeing the news that 'Jihadi John' was killed I felt an instant sense of relief, knowing he wouldn't appear in any more horrific videos.

"He was only a pawn in ISIS' stupid game but knowing it's over, that he's finally dead, still hasn't sunk in. As much as I wanted him dead I also wanted answers as to why he did it, why my dad, how did it make a difference?"

Meanwhile Diane Foley, James Foley — the first journalist killed by Emwazi — told ABC News that his murderer's potential death would be "really a small solace to us."

"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."

The strike came just as the United States seeks to increase pressure on Islamic State fighters, who have seized parts of Syria and Iraq, and who Obama has vowed to defeat.

The pressure includes US plans to deploy dozens of special operations forces to Syria, deliver more weaponry to U.S.-backed Syrian fighters and to thicken US air strikes against the militant group.

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