In the same breath, he said not allowing Syrian refugees into the US would betray American values.

Speaking at a news conference following G20 leaders' Summit here, Obama said US will continue working with other countries on a coordinated strategy to destroy the Islamic State without US combat troops.

The Islamic State has claimed responsibility of the Friday's attacks in Paris which killed 153 people and injured 350 others.

In pics: France in grief after terror attacks

"Not because our military could not march into Syria" or Iraq and "temporarily clear out ISIL, but because we would see a repetition of what we have seen before," he said, adding, "If you do not have local populations that are committed to inclusive governance and who are pushing back against ideological extremes, then they resurface."

Obama said US can presumably send 50,000 troops into Syria. "What happens when there is a terrorist attack generated from Yemen? Do we then send more troops into there?"

He said Paris killings were a 'terrible and sickening setback' in the fight against the Islamic State, also known as ISIS, ISIL and Daesh. But he insisted that the American-led strategy to 'degrade and destroy' the militant group is working.

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