Looking for His glorious appearing! Titus 2:13

It seems clear that Islamic State is raising the stakes, aware that the gruesome death of an American and the image of another one at the mercy of an executioner who is taunting a US president could invite retaliation - heavier air strikes at least.

But the United States and other Western powers may now be diverting their attention away from the Sunni insurgents in northern Iraq to what they are capable of doing overseas.

The group can draw on hundreds if not thousands of foreigners with Western passports that can keep them below the radar, like the British-sounding man who appeared to have killed Foley, to carry out its threats.

"The West are idiots and fools. They think we are waiting for them to give us visas to go and attack them or that we will attack with our beards or even Islamic outfits," said one.

"They think they can distinguish us these days - they are fools and more than that they don't know we can play their game in intelligence. They infiltrated us with those who pretend to be Muslims and we have also penetrated them with those who look like them."

"Many of the members of (Islamic State) that have come from abroad have come from Europe, from the U.S., from the Middle East and North Africa - all over the world," said Masrour Barzani, head of the Kurdish region's National Security Council.

"These are people that are not going to die in battles in Iraq and Syria. Many of these people will go back to their countries of origin, becoming potential leaders or terrorist operatives, which could really become a bigger threat to their own countries."

Western countries are well aware of the issue - nine people suspected of planning to join Islamist militants in Syria were detained in Austria on Wednesday - but can they come up with tactics to tackle it?

"We are absolutely aware that there are significant numbers of British nationals involved in terrible crimes, probably in the commission of atrocities, making Jihad with (Islamic State) and other extremist organizations," British Foreign Secretary Philip Hammond told the BBC.

"I don't think this video changes anything. It just heightens awareness of a situation which is very grave and which we've been working on for several months."

Jamal Khashoggi, a long-time expert on al Qaeda who interviewed Osama bin Laden, said that caution and concerns over security may have kept Islamic State from carrying out attacks on Western targets so far.

But under the right conditions it will not hesitate.

"If they can blow up a suicide bombers in Times Square this afternoon they'll do it. What is keeping them from doing that is vigilance and security," he said.

"But we have to admit that they are targeting all of us. If they can launch a terrorist attack in Riyadh, New York or London they'll do that."