The spokesperson for the Islamic Cultural Centre of Ireland has said he does not believe that there may be as many as 30 jihadists from Ireland who have fought in Iraq and Syria.

Dr Ali Selim said the figure was not accurate and wanted to know how the number was drawn up.

He said his members have not noticed any increased surveillance on their activities and said it was a "media sensation".

Dr Selim said it would be a "fatal mistake" to compare the Irish situation with that of the UK where there have been several documented cases of British citizens travelling to join Islamist fighters.

He said Ireland would not be similar because of the level of freedom and equality enjoyed here.

On reports that the Minister for Justice could revoke Irish passports for those engaged in jihadist type of activities, Dr Selim said that was not the way to tackle the problem.

He said that while he thought it was unlikely to be true, if Irish jihadists were found, they should be dealt with by education and rehabilitation.

Meanwhile, British Prime Minister David Cameron faced calls for changes to the law in an effort to combat the threat of Islamist extremism in the UK following the murder of US journalist James Foley.

Intelligence agencies on both sides of the Atlantic are working to identify the jihadist believed to have carried out the killing.

Analysts are sifting through the footage for clues amid suggestions that the Islamic State militant who carried out the killing is from London.

Politicians, the police and MI5 are concerned about the threat from British nationals who have travelled to Syria and Iraq to fight for IS returning to the UK to carry on their jihad.

Hundreds of Britons are believed to have travelled to the region, and "significant numbers" are believed to have been involved in "terrible crimes" and "probably in the commission of atrocities" according to British Foreign Secretary Philip Hammond.

Mr Cameron spoke about the threat to the UK when he returned to Downing Street following the release of the video of Mr Foley's murder.

He said "far too many" Britons had travelled out there and promised to "redouble" efforts to stop them going.

The jihadist in the execution video of Mr Foley is reported to be 'John', the ringleader of a trio of UK-born extremists responsible for guarding Western hostages and nicknamed after members of The Beatles, with the two others dubbed Paul and Ringo according to the BBC.

In the video of the murder of Mr Foley, US president Barack Obama was warned that the life of US hostage Steven Sotloff hinged on his "next decision".

The US has continued to launch air attacks on IS forces to shore up Kurdish and Iraqi efforts to hold the strategically important Mosul Dam.

British investigators are heavily involved in efforts to identify Mr Foley's killer and his group of extremists, with the eavesdropping agency GCHQ playing a vital role in intercepting any electronic communications between jihadists in Syria and Iraq.

The British agencies - MI5, MI6 and GCHQ - were also working with US and European counterparts and receiving reports from agents on the ground to try and build a more complete picture of the scenario in Iraq and Syria.

US Defense Secretary Chuck Hagel said US air strikes had helped to stall the IS advance in Iraq, but admitted that Washington needed to take a "cold steely hard look" at what other measures were needed.

"They are beyond just a terrorist group. They marry ideology, a sophistication of strategic and tactical military prowess, they are tremendously well-funded... this is beyond anything that we have seen," he said.

General Martin Dempsey, chairman of the US joint chiefs of staff, said IS was "an organisation that has an apocalyptic, end-of-days strategic vision and which will eventually have to be defeated".

"Can they be defeated without addressing that part of their organisation which resides in Syria? The answer is no. That will have to be addressed on both sides of what is essentially at this point a non-existent border."