The US Secret Service said it had detained the driver of a rented box truck that crashed into security barriers near the White House on Monday night, perhaps intentionally, but that there were no injuries or ongoing danger.
A Reuters witness said investigators found a Nazi swastika flag that apparently came from inside the truck, which crashed into barriers at Lafayette Square, adjacent to the White House grounds.
Officers retrieved the flag and plastic evidence bags that had been laid out on the sidewalk following the crash and placed them in the back of the U-Haul, a Reuters photographer said.
"Preliminary investigation reveals the driver may have intentionally struck the security barriers at Lafayette Square," Anthony Guglielmi, chief of communications for the Secret Service, said on Twitter.
US Park Police would file charges with investigative support from the Secret Service, he added.
WUSA television showed video of a box-type, U-Haul truck stopped alongside a row of steel bollards, with uniformed law-enforcement officers and a dog approaching the vehicle. A remote-controlled robot pried open the truck's rear door, revealing a dolly but no other obvious cargo.
Chris Zaboji, a witness to the crash, posted a brief video on social media showing the truck driving into the barricades. The video was verified by Reuters. After crashing once, the driver hit the barriers a second time, he said.
Zaboji, 25, an airline pilot who lives in Washington, said he had just finished jogging on the National Mall and was walking home when he heard a loud crash.
"I looked back and saw that the U-Haul van had rammed into the barricade. I backed away behind a guy on a golf cart and took the video on my phone. After I saw it rammed again I didn't want to be anywhere near the truck and left," Zaboji said.
A previous tweet from the Secret Service's Guglielmi said nobody from the White House or Secret Service was injured.
The exact location of President Joe Biden at the time was unclear. He met with Speaker of the US House of Representatives Kevin McCarthy at the White House earlier on Monday evening.
The nearby Hay Adams hotel was evacuated at the request of the Secret Service, the Washington Post reported, citing a hotel official, while the Secret Service said some roads and pedestrian walkways around the park were closed.
A spokesperson for the Washington Fire Department said a call came in at 9:40 pm (0140 GMT) for what was described as a suspicious package investigation.
Soon there was a major law-enforcement and public safety response, before investigators determined the contents of the mostly empty truck were harmless.