Story highlights Bernie Sanders says it's "impossible" to know how many Syrian refugees the United States should accept

He urged Middle Eastern countries like Syria, the United Arab Emirates and Turkey to do more to help refugees and fight ISIS

Washington (CNN) Vermont Sen. Bernie Sanders prodded Middle Eastern countries to aid refugees streaming out of Syria, but wouldn't say how many should be allowed into the United States.

"I think it's impossible to give a proper number until we understand the dimensions of the problem," the Democratic presidential contender said Sunday on NBC's "Meet the Press."

Sanders said Saudi Arabia and the United Arab Emirates should join Europe and the United States in helping to shoulder the burden of refugees driven from their war-torn countries amid the rise of ISIS -- and while he wouldn't give a number, Sanders said the United States should aid some of those refugees.

"People are leaving Iraq, they're leaving Syria, with just the clothes on their backs," he said. "The world has got to respond. The United States should be part of the response."

He's the latest Democratic contender to weigh in on the Syrian refugee crisis. Former Maryland Gov. Martin O'Malley has called for the United States to take in as many as 65,000 refugees next year, while Hillary Clinton has issued less specific calls for the United States to help those refugees.

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