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Police chiefs from across the nation testified before Congress today about the growth of radicalized individuals pledging to join ISIS – and what that means for first responders here at home.

A U.S. intelligence official confirmed to Fox News that 36,000 foreign fighters have now traveled to Syria from at least 120 countries.

“This means despite the 16-month bombing campaign, the number of foreign fighters has nearly doubled, along with the number of countries affected,” said chief intelligence correspondent Catherine Herridge.

Of that, at least 6,600 of suspected ISIS fighters hold Western passports – allowing them to travel to the U.S. without a visa.

Authorities are now pointing to gaps in official intelligence that could prove dangerous to those responding to domestic terrorism acts.

For example, local police now take charge of investigating reports of suspicious activity – but without intelligence from federal or overseas agencies, it may be impossible to act in a timely way, said Wally Sparks, Chief of the Everest Metro Police Department in Wisconsin.

“If the local law enforcement agencies are not aware of critical information pertaining to subjects in their community … Then we are missing a key piece of the preventative puzzle,” he said.

Watch more, above.

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