Washington, Sep 11 (IANS) Nearly six years after he entered the White House with a promise to end America's decade of wars, President Barack Obama has reversed course with a vow to strike the Islamic State terrorists "wherever they exist".

In a nationally televised address from the White House, a sombre looking Obama Wednesday night outlined a "steady, relentless" strategy to "degrade and ultimately destroy" the militant group with expanded airstrikes in Iraq as also neighboring Syria.

But even as he signalled a broader role for the US military, he suggested that "This mission will not be like the wars in Iraq and Afghanistan" and "will not involve American combat troops fighting on foreign soil."

"This effort will be a steady and relentless approach to take out terrorists who threaten us, while supporting our partners on the front lines," Obama said.

"I have made it clear that we will hunt down terrorists who threaten our country, wherever they are," he said. "That means I will not hesitate to take action against ISIL (as he called IS) in Syria, as well as Iraq.

"This is a core principle of my presidency: if you threaten America, you will find no safe haven."

Obama's speech from the White House also sought to convince allies of a firm US commitment to lead an international coalition to fight the Sunni militants variously known as ISIS, ISIL and Islamic State.

"America will lead a broad coalition to roll back this terrorist threat," he said. "Our objective is clear: We will degrade, and ultimately destroy, ISIL through a comprehensive and sustained counterterrorism strategy."

The president also announced another 475 American military advisers would go to Iraq, pushing the total figure to more than 1,000.

"We can't erase every trace of evil from the world, and small groups of killers have the capacity to do great harm. That was the case before 9/11, and that remains true today," Obama said.

IS poses a threat to the Middle East, including the people of Iraq and Syria, he said, adding: "If left unchecked, these terrorists could pose a growing threat beyond that region, including the United States."

Later in an email Obama outlined his four point strategy as: conduct a systematic campaign of airstrikes against these terrorists; increase support to the forces fighting them on the ground; working with partners prevent ISIL attacks; continue providing humanitarian assistance to the innocent displaced civilians.

"This is American leadership at its best: We stand with people who fight for their own freedom. And we rally other nations on behalf of our common security and common humanity," he said.

Commenting on Obama's speech, the New York Times said the President had "effectively set a new course for the remainder of his presidency and all but ensured that he would pass his successor a volatile and incomplete war, much like the one he inherited when he took office."

Obama's "plan may mark the first direct US intervention in Syria, a reversal of the White House's long-held resistance to becoming entangled in its 3-year-old civil war," said the Los Angeles Times.

The Washington Post called action against Islamic State a 'legacy issue' for Obama.

Noting that the president and his advisers have acknowledged that the campaign to defeat the Islamic State will take years, the influential daily said: "It is not a legacy the president expected to leave."