Watch President Trump being rushed out of news conference.
The Secret Service said the incident happened one block from the compound, when an officer fired on the suspect who had run "aggressively" towards him.
An agent then walked on stage as Mr Trump was speaking and led him away.
The president returned minutes later to say the situation was under control.
The US Secret Service said the incident happened on Monday on the corner of 17th Street and Pennsylvania Ave - outside the White House perimeter.
It said a 51-year-old man, who has not been identified, approached the officer, told him he had weapons and assumed a "shooter's stance", whereupon the officer shot him in the torso. Read more >>