Washington: The US Secret Service is investigating terrorist attack threats posted by an unknown user on the White House page in Facebook on Sunday, a spokesperson said.
At least three threatening messages appeared on the White House Facebook page amid heightened terrorist threat alert over the tenth anniversary of the September 11 terrorist attack, NBC News said.
"We`ll come back U.S.A. One day only 11/9/2011," one message said, featuring a photo of Osama bin Laden.
Another said: "We`ll come back 11/9/2011 to kill u all."
The messages were quickly removed, but the information was sent to the Secret Service`s internet threat desk.
"They process it, make an assessment and determine what the next step is," NBC News quoted Secret Service spokesman Ed Donovan as saying.
Law enforcement authorities in New York and Washington are on high alert against what was called by the authorities a "credible but unconfirmed" terror threat to the US a decade after 9/11 terrorist attacks, which killed 3,000 people.
White House Principal Deputy Press Secretary Josh Earnest said on Sunday the country`s special services have no new information on alleged preparations for a terrorist attack.