Waterloo, Iowa (CNN) Donald Trump's campaign speech in Waterloo, Iowa, was briefly interrupted Wednesday afternoon by a handful of hecklers that appeared to be climate change activists.

Trump was mid-speech at a local ballroom discussing the thousands of Syrians fleeing tumult in the country when several audience members holding up large red signs started to yell, "Mobilize now."

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Some of Trump's supporters did not take to the hecklers kindly, and at least one of them appeared to grab a sign away from the protesters.

The Republican presidential front-runner urged the crowd to remain calm, saying, "We want to be nonviolent towards those people." After the protesters were escorted out by police, Trump thanked the audience for not hurting them.

Trump's visit to Iowa comes as he continues to lead the Republican field in the state. He stands at 24% and is followed by retired neurosurgeon Ben Carson at 19%; former Hewlett-Packard CEO Carly Fiorina at 8%; and former Florida Gov. Jeb Bush at 7%, according to a new NBC News/Wall Street Journal poll.