WEST PALM BEACH, Fla. (CBS12) -- FBI Director Kash Patel announced that a hunting stand found within sight of the Air Force One landing zone is the reason Southern Blvd. remains sealed off.

Southern Blvd. between Congress Ave. and Military Trail was shut down Saturday afternoon, and shortly after, the Palm Beach County Sheriff's Office (PBSO) announced it was closed for an FBI investigation.

"Prior to the President's return to West Palm Beach, USSS discovered what appeared to be an elevated hunting stand within sight line of the Air Force One landing zone," Patel told Fox News Digital. "No individuals were located at the scene. The FBI has since taken the investigatory lead, flying in resources to collect all evidence from the scene, and deploying our cell phone analytics capabilities."

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U.S. Secret Service (USSS) communications chief Anthony Guglielmi said agents came across the stand while conducting "advance security preparations" ahead of Trump's arrival at Palm Beach International Airport. Fox News reported that a law enforcement source said the stand appeared to have been set up "months ago."

Motorists are still being urged to avoid the area and use alternate routes.