An apparent smoke bomb was thrown over the fence of the White House as hundreds of Occupy protesters massed outside the gates.
The crowds were dispersed on Tuesday night (local time), and U.S. Secret Service spokesman George Ogilvie says there were no arrests in the incident.
However, people inside the White House were being prevented from exiting on the Pennsylvania Avenue side of the building as the situation was being resolved.
Mr. Ogilvie says there were 1,000 to 1,500 protesters at one point. He said something appearing to be a smoke bomb was thrown over the fence and that the device was being removed.