(CNN) -- America's top defense officials left open the possibility of targeting ISIS fighters in Syria, saying during a news briefing Thursday that it was not enough to just hit the extremist group in Iraq. Defense Secretary Chuck Hagel and Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, stopped short of calling for U.S. military action in eastern Syria, an ISIS stronghold. "Can they be defeated without addressing that part of the organization that resides in Syria? The answer is no," Dempsey said during the briefing at the Pentagon. Repeatedly pushed by reporters about whether that meant operations against ISIS in Syria, Hagel said, "We're looking at all options."
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ISIS is "a cancer" that can spread into Europe and the U.S., Sen. John McCain says
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"This is beyond anything we have seen," Defense Secretary Chuck Hagel says
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Dempsey says ISIS can't be defeated without addressing its presence in Syria
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U.S. Central Command has conducted 51 airstrikes near the Mosul Dam
"We are grateful to the men and women of the @placeholder armed forces who have carried out these decisive attacks against the terrorist forces of ISIS," said a statement from the regional government.