UK Foreign Secretary has confirmed the ISIS militant who beheaded US journalist James Foley “appears to be British” after his mother posted a heartbreaking tribute to her son.

Foreign Secretary Philip Hammond said the Islamic State was waging war on Britain and the West and the organisation had to be dealt with “on that basis”.

He added that the Government believed the video was “genuine”.

Mr Hammond said Britain would oppose the Islamic State “with every breath in our body” and could send British troops to Baghdad, as UK Prime Minister David Cameron cut his holiday short to return to Downing Street for talks.

Mr Hammond voiced his “absolute horror” at the apparent beheading which he said showed the “brutality” of Islamic State jihadists.

“It just is one more example in a catalogue of brutality by this organisation.” He said IS “atrocities” in Iraq and Syria were “completely horrifying and shocking” and were driving the international community’s efforts to support Iraqis and Kurds in pushing back against the “evil organisation”.

The masked executioner in the video speaks English with a British accent. “On the face of it, it appears to have been a British person. We’ll have to do some more analysis to make quite certain that that is the case,” Hammond said.

The news comes after Foley was forced to deliver a brutal message to his family just moments before he was beheaded by ISIS militants.

Foley, who was kidnapped while reporting on the conflict in Syria in 2012, was beheaded by extremists who warned there would be more executions unless the US and President Obama bowed to their demands.

Unconfirmed video and pictures of the photojournalist’s heartbreaking final moments emerged this morning via Twitter accounts claiming to be associated with the Islamic State, previously known as the Islamic State in Iraq and Syria (ISIS).

In what looked like a prepared statement, Foley called on his family to rise up against the US, who he calls his “real killers”.

“I call on my friends, family, and loved ones to rise up against my real killers, the US government, for what will happen to me is only a result of their complacency and criminality,” he said.

“My message to my beloved parents - save me some dignity and don’t accept any meagre compensation for my death from the same people who effectively hit the last nail in my coffin from their recent aerial campaign in Iraq.”

CAPTIVE: James Foley spoke about an earlier capture and detention by Gaddafi forces

More tributes have flowed in for Foley, from reporters who worked with him.

Javier Espinosa, who was freed by an Islamist group in Syria tweeted:

RIP #JamesFoley, a great journalist and a great human being #ISIS #Syria — Javier Espinosa (@javierespinosa2) August 19, 2014

Another tweeted:

I was w/ James Foley in Aleppo, August 2012 for a day in #Selahaddin. Syrian opposition members were adoring him. He was a kind, brave man — ilhan tanir (@WashingtonPoint) August 19, 2014

Mr Foley, 40, was abducted while covering the campaign against President Bashar al-Assad. He worked for a variety of media organisations including the AFP news agency.

The gruesome video, titled “A Message to America”, was originally uploaded on Tuesday but has since been deleted.

Prime Minister Tony Abbott said today he was sickened by the news of the beheading.

Although he had not seen the video he was appalled by the reports.

“It’s absolutely sickening, absolutely despicable,” he told Brisbane’s 4BC radio. “It’s a sign that there can be no compromise whatsoever with the murderous terrorists of the ISIL movment. This is as near to pure evil as we are ever likely to see.”

Here's a picture of journalist James Foley, via @TheWire. Let's remember him like this. pic.twitter.com/Lc2ymzoCRj — Ismat Sarah Mangla (@ismat) August 19, 2014

EXECUTION’S BRUTAL MESSAGE

The gruesome video shows Mr Foley wearing orange prisoner fatigues being led to a remote desert location where he is forced to kneel before reciting a message urging Americans to rise against his “real killer” — the United States.

“I call on my friends, family, and loved ones to rise up against my real killers, the US government,” he is heard to say. “For what will happen to me is only a result of their complacency and criminality.

The US government issued a statement saying the intelligence community was working to formally verify the identity of the men shown in the footage.

“If genuine, we are appalled by the brutal murder of an innocent American journalist and we express the deepest condolences to his family and friends. We will provide more information when it is available.”

TERROR PROPAGANDA TARGETS FAMILY

In the video Mr Foley looks calm as he kneels with his hands tied behind his back. Speaking in a level voice with a a microphone attached to his orange robe, he can sometimes be heard swallowing as he continues his speech.

Do not watch the video. Honor James Foley's memory. He was a good damn reporter. The world is less good without him. — Jeb Boone (@JebBoone) August 19, 2014

“I call on my brother John, who is a member of the US air force. Think about what you are doing, think about the lives you destroy, including those of your own family.”

He goes on to attack recent US airstrikes on Iraq: “Think John, who did they really kill? And did they think about me, you, our family when they made that decision?”

His statement, which is presumed to have been prepared for him by the militants, ends with: “I guess all in all I wish I wasn’t American.”

This morning in a Facebook message to supporters, Foley’s mother Diane bravely ignored the propaganda message her son had been forced to read.

“We have never been prouder of our son Jim.

“He gave his life trying to expose the world to the suffering of the Syrian people.

“We implore the kidnappers to spare the lives of the remaining hostages. Like Jim, they are innocents. They have no control over American government policy in Iraq, Syria or anywhere in the world.

“We thank Jim for all the joy he gave us. He was an extraordinary son, brother, journalist and person. Please respect our privacy in the days ahead as we mourn and cherish Jim.”

It’s not the first time Foley has been held captive. He was taken by government forces in while covering the 2011 uprising against Libya’s Muammar Gaddafi. He was released after six weeks.

In May 2011, James Foley recounted his ordeal after being freed from captivity in Libya http://t.co/99VrRz8c3Y pic.twitter.com/2ek5otR7ps — The Boston Globe (@BostonGlobe) August 19, 2014

In the ISIS video, Foley is beheaded with a knife by a black-masked man who speaks with what sounds to be a British accent.

“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 executioner intones.

Instead of spreading the image and video of that horrible act, here's James Wright Foley. Remember him and his work. pic.twitter.com/dAJVNYejys — Naudia Zaki Vanelli (@naudsie) August 19, 2014

The Islamic State has issued a warning with the video: There will be more executions if President Obama does not end air strikes in aid of the embattled Kurdish and Iraqi Government forces.

“We will drown all of you in blood,” the jihadists state.

TWO MORE CAPTIVES THREATENED

The propaganda video also shows what it claims to be another US captive, identified as journalist Steven Joel Sotloff.

The dialogue then states his future depends on President Obama’s “next decision”.

Mr Sotloff is a freelance journalist who was abducted in Syria in August 2013.

A third prisoner has been threatened in a separate statement attributed to the Islamic State and addressed to his family.

Warren Weinstein is named as a prisoner the jihadists wish to exchange for one of their own members held by unnamed Western-affiliated forces.

Friend and fellow journalist Steven Sotloff who appears alive at the end of that video...I'm without words. — Iona Craig أيونا (@ionacraig) August 19, 2014

The open letter, circulating on Twitter, threatens that if Mr Weinstein’s family do not oppose their government, their son will suffer.

“Your continued silence on the inaction of your government will only lead to your prisoner dying a lonely death in prison after this deliberate and prolonged neglect on the part of your government,” the document reads.

“Therefore, if you want Warren Weinstein to be released; do whatever you can to pressurize your government”.