Washington DC - A gunman opened fire near the White House on Saturday evening, with Secret Service agents killing the assailant in a shoot-out during which a bystander was also struck, authorities said.

President Donald Trump was in the White House at the time – on a day when he was working to negotiate a deal with Iran – but was not impacted by the incident, Secret Service communications chief Anthony Guglielmi said in a statement.

The confrontation took place just after 6:00 PM (2200 GMT) when a man near the White House security perimeter "pulled a weapon from his bag and began firing."

"Secret Service Police returned fire striking the suspect who was transported to an area hospital where he was pronounced deceased. During the shooting one bystander was also struck by gunfire," Guglielmi said, without giving details on the bystander's condition.

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No Secret Service officers were hurt.

"Thank you to our great Secret Service and Law Enforcement for the swift and professional action taken this evening against a gunman near the White House, who had a violent history and possible obsession with our Country’s most cherished structure," Trump said on Truth Social early Sunday.

Multiple media outlets identified the suspect as Nasire Best (21) of Maryland, reporting that Best had a history of mental health concerns and had multiple prior interactions with Secret Service members.

Police and security forces swarmed the scene, cordoning off access as National Guard troops blocked an AFP reporter from entering the area in downtown Washington.

"We heard probably 20 to 25 what sounded like fireworks, but they're gunshots, and then everyone started running," Canadian tourist Reid Adrian told AFP.

Journalists who were on the White House North Lawn at the time said they were ordered to run and shelter in the press briefing room.