02/22/2012 05:07 pm ET Updated Feb 22, 2012

Jon Stewart, Stephen Colbert Receive Messages Threatening Congress

WASHINGTON - A U.S. law enforcement official said on Wednesday that officials are probing letters sent to television personalities Jon Stewart and Stephen Colbert, which threaten biological attacks on U.S. senators.

The official, speaking on condition of anonymity, said the messages to Stewart and Colbert threatened to send letters to all 100 U.S. senators, and that 10 of them would contain a deadly pathogen.

Several letters have been received at lawmakers' offices, and so far the substance they contained has been found to be harmless, a Senate official said.

Other law enforcement officials said some of the letters in question contained anti-government and anti-Wall Street rhetoric.

(Reporting by Mark Hosenball; Writing By Warren Strobel; Editing by Sandra Maler)