Martin Dempsey
Martin DempseyReuters

The chairman of the U.S. Joint Chiefs of Staff, General Martin Dempsey, left the door open Thursday to stepped-up U.S. military involvement in Iraq if the Islamic State of Iraq and the Levant (ISIS) poses a threat to the United States.

"Assessing and advising and enabling are very different words than attacking, defeating and disrupting," CNN quoted Dempsey as having said during a briefing at the Pentagon in Washington.

"We may get to that point if our national interests drive us there, if (the Islamic State in Iraq and Syria) becomes such a threat to the homeland that the President of the United States, with our advice, decides that we have to take direct action. I am just suggesting to you that we are not there yet."

"We will match the resources we apply with the authorities and responsibilities that go with them based on the mission we undertake, and that is to be determined," he said.

Terrorists, spearheaded by ISIS and joined by supporters of executed dictator Saddam Hussein, have overrun a large chunk of northern and north-central Iraq over the past several weeks.

President Barack Obama, while initially said he would not send troops to Iraq, later announced he would send 300 troops to the country to operate as “advisers” to the Iraqi forces.

A Pentagon official said last week that the United States has started flying armed drones over Baghdad, but stressed the armed drones are to provide protection of U.S. interests and that Obama still has not authorized airstrikes against the ISIS rebels.