Ahead of America's 250th birthday this weekend, agencies are prepared for the possibility of an attack on Fourth of July crowds and parade-goers.

That includes the Salute to America 250 Celebration and Fireworks in Washington, D.C., which the White House saids will be "one of the grandest displays of patriotism that the world has ever seen."

More than a million people are slated to gather on the National Mall to hear President Donald Trump speak and watch "the largest pyrotechnics display in the history of the world," the White House said.

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Jason Pack, a retired supervisory special agent with the FBI, told Fox News Digital agencies have likely been preparing and coordinating for the event for weeks, if not months.

"It's a whole of government approach, not just one agency," Pack said. "That's really important because that's how in the past [threats] were stovepiped and could have gotten missed."