New Delhi: A US Secret Service spokesman on Wednesday said that the White House was locked down after a smoke bomb was thrown over its fence as hundreds of Occupy protesters massed outside the gates.
He said that the authorities were investigating the smoke bomb tossed over fence.
The crowds were dispersed on Tuesday night and US Secret Service spokesman George Ogilvie said 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.
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.
US President Barack Obama had taken his wife Michelle to a restaurant for a dinner on the occasion of her 48th birthday.
The First Couple have since returned to the White House without any difficulty.
The journalists who were travelling with the President on return were prevented from leaving the grounds.
US Secret Service was investigating the object that was thrown over the fence.
After holding in the briefing room for 45 minutes, a White House official escorted the press corps out of the White House grounds through the Executive building and out to an exit on 17th Street.
No arrest have been made so far and the US Secret Service was investigating the incident.
(With additional inputs from agencies)