President Barack Obama vowed to punish the Islamic State killers of American journalist James Foley on Tuesday but said rooting out the militant group in Iraq and Syria will not be fast or easy.
As Obama spoke, the United States was moving ahead with surveillance flights over Syria to identify targets for a potential presidential order to launch air strikes against Islamic State targets in what would be a direct US military intervention into a country embroiled in a three-year civil war.
"America does not forget. Our reach is long. We are patient. Justice will be done," Obama told veterans gathered at a convention of the American Legion in Charlotte, North Carolina.
Obama, who ordered air strikes against the militant group in Iraq and is considering them for Syria, said he would do whatever is necessary to go after those who harm Americans.
"Rooting out a cancer like ISIL won't be easy and it won't be quick," he said. ISIL is the acronym the United States uses for Islamic State.
Launching air strikes into Syria would add an unpredictable element to a civil war that Obama has taken great pains to stay out of a year after stepping back from attacking the government of Syrian President Bashir al-Assad for using chemical weapons on his own people.
White House spokesman Josh Earnest said there was no plan to coordinate with the Syrian government on how to counter the threat from Islamic State. Syria has appealed for coordination.
"As a matter of US policy we have not recognized the Assad regime as the leader of Syria. There are no plans to change that policy and there are no plans to coordinate with the Assad regime as we consider this terror threat," he said.
Obama was provoked into action by the release of a graphic video last week showing the beheading of Foley by Islamic State fighters.
A decision by Obama to launch air strikes in Syria did not appear to be imminent.