The White House was placed on lockdown on Thursday after two people threw unspecified items over the north and south fences, NBCNews.com reported.
Both suspects threw the items at the same time, according to the Secret Service. Each suspect is in custody as officials determine if the objects are dangerous or not.
The names of the suspects have not been released.
President Barack Obama was not in Washington at the time of the incident; he is currently in California on a fundraising trip.
Officials are unsure of when the lockdown will be lifted and neither suspect has been transported off of the property yet, NBCNews.com said.
This is the second lockdown in the past three days. On Tuesday, a man was detained after following a car carrying the president's daughters.
The driver was later identified as 55-year-old Mathew Evan Goldstein. He held a pass for the U.S. Treasury Building, which is located next to the White House, a source close to the incident told CNN.
According to Reuters, Goldstein is an employee of the Internal Revenue Service.
The lockdown was lifted an hour later after the car was checked for explosives. No one was able to leave or enter White House grounds during that time.
In February, the White House was locked down when a man tried to jump over the fence. The lockdown was lifted after the man was searched and taken into custody.
