BRISBANE, Australia (AP) -- President Barack Obama reiterated his desire not to send U.S. combat troops to fight Islamic State fighters, but said there are always circumstances where the U.S. might need to deploy ground troops.

President Barak Obama speaks to the media during a press conference at the end of the G-20 summit in Brisbane, Australia .(AP Photo/Rob Griffith)

He cited a hypothetical example in which Islamic State fighters obtain a nuclear weapon. He said under such a scenario he would not hesitate to order troops into combat.

"So the question just ends up being, what are those circumstances?" he said during a news conference as he wrapped up a week-long trip to Asia and Australia. "Right now we're moving forward in conjunction with outstanding allies like Australia in training Iraqi security forces to do their job on the ground."

Obama was responding to a question about remarks by Army Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, last week that troop deployments in the fight against Islamic extremists were an option under consideration.

"That's his job -- to think about various contingencies," Obama said.

Obama also pushed back against reports he was pursuing a review of his strategy toward Syria and President Bashar Assad. He says nothing like that has taken place. But he said his administration is always reviewing his broader strategy against the Islamic State.

Obama said that while Assad has ruthlessly murdered hundreds of thousands and has lost legitimacy, he said he said he was not considering ways to remove Assad from office.

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