The Secret Service said that "during the course of the encounter and subsequent arrests, the individuals posed no immediate danger to any Secret Service.”
At approximately 5:24 p.m., police said a man and a woman approached Secret Service officers "on their own accord" outside of a secured vehicle checkpoint of the White House complex past the western-most crosswalk of 15th Street at Pennsylvania Avenue NW, NBC News reported.
One person said "they were there to meet with the President of the United States and had a letter to deliver to him," police said.
"One of the individuals disclosed the possession of a weapon and was immediately detained and the second individual disclosed the location of an additional weapon in a vehicle nearby," a Secret Service spokesperson said.
After finding that vehicle, the Secret Service said its officers "took possession of the weapon."
The man, who has not been identified, was arrested for possession of a BB gun.
MA/PR