Speaking at a NATO summit, Obama said that United States would also try to involve Middle Eastern allies in a strategy to counter the jihadists, who have overrun large swathes of territory.
"It's not going to happen overnight but we are steadily moving in the right direction and we're going to achieve our goal," Obama said.
The President said that regional involvement was ‘absolutely critical’ - although the state department said that Washington had ‘no plans’ for any military coordination with Iran in the fight.
"We're going to degrade and ultimately defeat ISIL," Obama added, using the previous name of the Islamic State, which has claimed responsibility for videos showing the beheading of two US journalists.
The executions appear to be carried out by the same British English-accented militant, who also threatened to kill a British hostage unless US air strikes in the regions were halted.

In a further reminder of the brutality in Iraq, Iraqi Kurdish forces and Shiite militias on Friday discovered mass graves containing 35 bodies after retaking the town of Sulaiman Bek from jihadists.
Iraqi forces, militiamen and Kurdish fighters broke a months-long jihadist siege of the town of Amerli on Sunday and retook Sulaiman Bek the following day, in the first major successes for the federal government since the crisis began.
Obama said that he was ‘confident’ a coalition was being formed with US officials saying the plan was to have a strategy in place by the start of the United Nations general assembly later this month.
Obama said that there was ‘unanimity’ among NATO members that the group ‘poses a significant threat’, although many cautioned that any action hinged on the formation of a new Iraqi government.
Kerry on Friday co-chaired with Britain a meeting of ministers from Australia, Canada, Denmark, France, Germany, Italy, Poland and Turkey in a bid to win support for the fight against IS.

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