A smoke bomb was hurled inside the White House complex, prompting the Secret Service to deploy a robot to check it out. President Barack Obama and his wife were not at home, media reports said.
A 'smoking object' was thrown over the White House fence late Tuesday, and authorities were investigating it, CNN quoted US Secret Service spokesman George Ogilvie as saying.
The president and his wife Michelle Obama were not in the White House as they were celebrating her birthday at a restaurant a few blocks away.
Ogilvie said the unidentified object was thrown during a protest.
Occupy protesters rallied at the White House, Capitol Hill and at the Supreme Court Tuesday.
Fox News reported that one or more smoke bombs may have been thrown over into the heavily-guarded White House.
The Secret Service also deployed a robot to check out the devices on the North Lawn.
The Occupy movement began in September seeking action against unequal distribution of wealth.