Martin Dempsey, chairman of US Joint Chiefs of Staff, said during a Pentagon press briefing that IS terror group has an "apocalyptic, end-of-days" vision that will eventually have to be defeated, Xinhua reported.
And to defeat the terror group, they must be defeated not only in Iraq, but Syria as well, the officer said.
"They will have to be addressed on both sides of what is at this point a non-existent border," Dempsey said. "That will come when we have a coalition that takes on the task of defeating IS over time."
The chairman said he preferred to call the group ISIS because it highlights the terrorists' long-term goals. ISIS stands for the Islamic State of Iraq and Syria.
The threat from IS is a serious representation of the threat from terror groups, Dempsey said.
The US role in this long contest will be complicated. The country must participate in this contest of ideologies, particularly in a leadership role, Dempsey said.
There are three military tools America will use, Dempsey said.
"One is direct action. There will be cases where we are personally threatened, US persons and facilities are threatened, that we will use direct action," he said.
The second is building partner capacity, and that has to be a main avenue of advance, the chairman said.
The third tool is to enable partners, "which is what you see us doing somewhat now in Iraq with both the Iraqi security forces and the Peshmerga," Dempsey added.