London, Asharq Al-Awsat—The grisly on-camera execution of an American journalist by the Islamic State of Iraq and Syria (ISIS) was likely carried out by a British national, the UK’s Foreign Secretary said on Wednesday.

During an interview on BBC Radio, Philip Hammond said the ISIS fighter who beheaded kidnapped freelance photojournalist James Foley “on the face of it appears to have been a British person.”

In the video, which was posted online on Tuesday, an ISIS fighter dressed in black appears standing over Foley in an arid, desert location. After reciting a statement saying his execution is a result of US bombing of ISIS targets in Iraq, Foley is apparently beheaded by the ISIS fighter.

Before the killing, Foley’s killer, speaking in a British accent, says: “You [the US] are no longer fighting an insurgency. We are an Islamic army and a state that has been accepted by a large number of Muslims worldwide . . . any attempt by you, Obama, to deny the Muslims their rights of living in safety under the Islamic caliphate will result in the bloodshed of your people.”

The video then shows another hostage, believed to be the missing American reporter Steven Sotloff, and warns that he will also be killed if US strikes on ISIS targets continue.

Foley was seized by unidentified armed men in November 2012 while covering the conflict in Syria. His whereabouts remained unknown until now. Sotloff was seized in Syria last year, close to the Turkish border.

The video of Foley’s killing is likely to refocus attention on the role of Western Muslims in the conflicts raging in Syria and Iraq.

Hammond told the BBC: “We’ve been saying for a very long time that there are significant numbers of British nationals in Syria, increasingly in Iraq, and one of the reasons why what is going on in Syria and Iraq is a direct threat to our own national security is the presence of significant numbers of our nationals who may at some stage seek to come back to the UK with the skills, the tradecraft that they’ve learned working with these terrorist organizations, potentially posing a threat to our domestic security here in the UK.”

Following the publication of the video, British Prime Minister David Cameron announced he was cutting his holiday short and returning to London.

A statement from the prime minister’s office said: “If true, the brutal murder of James Foley is shocking and depraved.”

“[The prime minister] will meet with the Foreign Secretary and senior officials from the Home Office, Foreign Office and the agencies to discuss the situation in Iraq and Syria and the threat posed by [ISIS] terrorists.”

Hammond subsequently told Sky News that British and US intelligence services would begin work on trying to identify the man shown killing Foley.

“Our intelligence services will be looking very carefully on both sides of the Atlantic at this video to establish its authenticity, to try to identify the individual concerned, and then we will work together to try to locate him,” he said.

A number of citizens of the US and member-states of the EU have been convicted of either traveling or attempting to travel to Syria to take part in the fighting there, while in April the EU’s most senior counter-terrorism official warned that around 500 Europeans were fighting in Syria.

As ISIS operates in both Iraq and Syria, it is likely that the organization’s European members will also begin to play an increasingly prominent role in Iraq.

Speaking to the BBC on Wednesday, Shiraz Maher, a senior fellow at King’s College London’s International Centre for the Study of Radicalization, said: “Unfortunately the British participation in the conflict raging in both Syria and Iraq is one of full participation.”

He added: “Unfortunately, they are some of the most vicious and vociferous fighters who are out there.”