The White House was put "on lockdown" due to an investigation into a suspicious package nearby, according to reports.
The item was in nearby Penn Avenue and US Secret Service officers said they were "responding to an incident involving a suspicious package".
A number of reporters in Washington described the residence as being on lockdown and said they were being assembled in a briefing room on Monday afternoon.
Megan Pratz, a reporter for Cheddar, said: "We are literally locked in here. We can't see much but Secret Service officers just ran across the lawn."
She later added: "Despite the Oval Office announcement from the President, the White House is still under lock down."
An update from the US Secret Service, posted on Twitter, said: "Secret Service Uniformed Division Officers are responding to an incident involving a suspicious package located on Pennsylvania Ave.
"Pedestrian traffic is closed along Pennsylvania Ave. between 15th and 17th streets to include Lafayette Park."
The Service later said the package had been declared safe.
Reporters had gathered at The White House as President Donald Trump signed a deal imposing new sanctions on Iran which target the country's supreme leader, amid an escalation in tensions between the two countries.
