The driver, Thomas Richard Ross, of New Waterford, Ohio, was injured in the crash, but nobody else was hurt, they said.
The truck was moving erratically and ran eight or nine red lights before a Pittsburgh police officer pulled it over late yesterday morning near the FBI building on the city's South Side, authorities said.
The driver initially refused to surrender and was "acting erratically, claiming to have a bomb," and although he later acted as though he was going to surrender he instead floored the gas pedal and rammed the gate, the Pittsburgh public safety department said.
FBI agents checked the truck for bombs and other weapons that might signal an intended attack and found nothing.
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"There's no nexus to terrorism at all from what we know now," Heeb said. "There's no reason to believe that was the case."
Ross faces numerous charges including aggravated assault, recklessly endangering another person, fleeing and eluding and various driving offenses, the Pittsburgh public safety department said.
Local authorities said they were working with the FBI on the case. Heeb said the main focus was the driver's mental state and his history.