About four bridges in California are believed to be possible targets of further terrorist attacks.
The Golden Gate Bridge near Marin County in California is shrouded in early morning mist
He said that information "from several different sources" spoke of a possible attempt to blow up the bridges during the rush hour between November 2 and 7.
He said that the bridges wouldn't be closed, and it was up to commuters to decide whether to drive over them in the coming days.
The bridges at risk include the Golden Gate and Bay Bridges in San Francisco, the Vincent Thomas Bridge in Los Angeles and the Coronado Bridge in San Diego.
Security was tightened at The Golden Gate after the September 11 attacks, with pedestrian and bicycle traffic barred from the bridge for several weeks.