US Secret Service deputy director Matt Quinn said a bystander was struck by the suspect.
Quinn said the motorcade of Vice President JD Vance went through the area not long before the shooting, but there was no indication it was the target.
The incident happened on Monday afternoon local time in the National Mall.
A spokesman for the DC Fire and EMS Department said emergency units transported an adult male to the hospital, and were treating what appeared to be a teenage male for minor injuries.
The Secret Service encouraged people to avoid the area as emergency crews responded to the shooting not far from the White House, where President Donald Trump was holding a small business event.
The White House was briefly locked down as authorities investigated the incident.
The Secret Service ushered journalists who were outside into the briefing room, and Trump continued his event without interruption.
"US Secret Service personnel are on the scene of an officer-involved shooting at 15th Street and Independence Avenue in Washington, DC. One individual was shot by law enforcement; their condition is currently unknown," the Secret Service said in a statement on social media platform X.
The DC Police Department said police were on the scene of the probe.
"The scene is secure. Avoid the area as roads will be closed for several hours," police said in a statement.
Law enforcement have been on alert in recent days in the US capital following a shooting at the White House Correspondents' Association Dinner in late April over which a suspect has been arrested.
with AP
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