“No just God would stand for what they did yesterday and what they do every single day,” said the President. “ISIL [the Islamic State of Iraq and the Levant] has no ideology of any value to human beings. Their ideology is bankrupt,” he said.

In the video militants of the group also known simply as the Islamic State said they acted in response to US air strikes against them in Iraq.

In the footage after Mr Foley is murdered the camera turns on to another missing US journalist, Steven Sotloff. A masked militant says that Mr Sotloff’s future depends on Mr Obama’s “next decision”.

In his statement Mr Obama offered no suggestion that US strategy in Iraq would change.

“The United States of America will continue to do what we must do to protect our people,” he said. “We will be vigilant and we will be relentless. When people harm Americans anywhere, we do what’s necessary to see that justice is done and we act against ISIL, standing alongside others.”

He paid tribute to Mr Foley as a courageous journalist who sought to tell the story of the people of Syria, and by contrast described the militants of the Islamic State who took his life as nihilistic cowards.

“They may claim out of expediency that they are at war with the United States or the West, but the fact is they terrorise their neighbours and offer them nothing but an endless slavery to their empty vision and the collapse of any definition of civilised behaviour.”

Mr Obama offered a prayer “for those who loved Jim” and for “those other Americans who are separated from their families.” According to the Committee to Protect Journalists 69 journalists have died covering the Syrian civil war that gave rise to the IS, more than 80 have been kidnapped and approximately 20, both local and international, are currently missing in Syria.

Siting unnamed US officials Associated Press reported that US military planners “weighed the possibility” of sending a small number of additional troops to Baghdad.

So far Mr Obama has insisted that the way to secure a lasting defeat of IS, a Sunni militant group, was to reform the Shiite-dominated Iraqi government. To that end the US has supported the removal of the former prime minister, Nouri al-Maliki, in the hope his replacement, Haider al-Abadi, might prove to be more inclusive and limit Sunni support for the IS.

The US is also engaged in air strikes in Iraq, which it says is limited to protecting US interests and humanitarian relief for those threatened by IS, but pressure is increasing on Mr Obama from some quarters to broaden the US strategy in Iraq to destroy the IS.

On Tuesday in the US the Defence Department announced it had conducted 14 air strikes in the vicinity of the Mosul dam earlier in the day, destroying or damaging six IS Humvees, three roadside bomb implacements, one mortar tube and two armed trucks.

Military strategist, Stephen Biddle, professor of international affairs at George Washington University and senior fellow at the Council on Foreign Relations, told Fairfax he believed the murder of Mr Foley was designed in part to provoke the US and drag it deeper into the conflict in Iraq, which is essentially a civil war. He said it appears the IS is seeking to cement its support among Sunnis and portray the Shiite dominated Baghdad government as a US puppet.

The IS video prompted an international campaign to prevent the spread of the IS video by social media. On Twitter there were thousands of calls for people to share photos of Mr Foley at work, rather than the IS video of his death.

Twitter announced it would close the accounts of people sharing the IS video, but despite complaints it has not taken action against the New York Post, which ran a front page photo of Mr Foley with a knife to his throat moments before his murder.