US military leaders have said the strength and sophistication of Islamic State militants pose a imminent threat to the United States.
Their violent tactics including the beheading of American journalist James Foley have been met with horror.
US officials are worried about the possibility that European and US nationals would return to their home countries after being radicalised fighting for IS in Iraq and Syria.
“They’re 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’ve seen, so we must prepare for everything, and the only way you do that is you take a cold, steely hard look at it and get ready,” said Chuck Hagel, US Defence Secretary.
Washington has not ruled out escalating cross-border military action in order to defeat IS, which has taken control of large swathes of Syria and Iraq this summer.