FOX has learned exclusively that the FBI has caught a suspect intending to conduct a terrorist attack at the U.S. Capitol.

Update: The suspect has been charged with attempting to use a weapon of mass destruction.  He's been in the United States illegally since 1999 when his tourism visa expired.

FOX News Radio's Rich Johnson has details in Washington:

The FBI has arrested a Moroccan man just a couple of blocks from the Capitol. A man carrying what he believed was a vest packed with explosives.

His goal -- set it off inside the Capitol Building.

But FOX News has learned the man appears to be another would-be terrorist who was thwarted by undercover agents, who gave him what a vest that was actually harmless.

Officials say the public was never in danger, and the man's been under surveillance for some time.

In Washington, Rich Johnson, FOX News Radio

READ the official statement from the United States Capitol Police:

USCP / FBI Arrest

On Friday, February 17, 2012, members of the U.S. Capitol Police and the FBI arrested an individual in the area of the U.S. Capitol.  This arrest was the culmination of a lengthy and extensive operation during which the individual was closely and carefully monitored.  The U.S. Capitol Police was intimately involved in the investigation for the duration of the operation.  At no time was the public or Congressional community in any danger.