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Trump returned to the briefing room after several minutes on Monday (local time) and said a person was shot by law enforcement and has been taken to the hospital.
The Republican president said he understood the suspect had been armed.
"It was a shooting outside of the White House," Trump said.
"It seems to be very well under control. ... But there was an actual shooting, and somebody has been taken to the hospital. I don't know the condition of the person."
No one else was wounded in the shooting, Trump said.
The president praised the Secret Service response and said the agency would have more details on the event later.
"There were no details - we just found out just now," Trump told reporters.
The Secret Service did not immediately respond to queries about the incident.
Minutes into a news briefing, Trump was taken out of the room with no explanation for the disruption.
Treasury Secretary Steven Mnuchin and Office of Management and Budget Director Russ Vought were also taken out of the room and the doors were locked.
Trump told reporters he was taken to the Oval Office outside the briefing room after he was escorted out.