Concern about Islamic extremism is on the rise around the globe, according to new polling data from the Pew Research Center.

According to the global survey — which was conducted before Thursday's killing of four Marines in Tennessee as well as a set of attacks across three continents in June — 53 percent of Americans say they are "very concerned" about Islamic extremism in the U.S., up from 36 percent in 2011.

Similar numbers persist in many European nations, which have seen 20- and 30-point increases in the number of people reporting grave fears about extremist violence.

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