The FBI and NYPD are investigating threatening letters that claim to contain dangerous pathogens sent to media companies and U.S. senators, law enforcement officials tell NBC New York.

According to law enforcement officials, the person sent letters to Jon Stewart and Stephen Colbert, of “The Daily Show” and “The Colbert Report,” claiming more letters had been sent to 100 senators and various media companies, including The New York Times, Fox News and NPR.

The writer, who voices anger over corporate greed and the state of the U.S. economy, said some of the letters contained harmful substances at random.

The letters are believed to have been mailed from Oregon and are signed “MAB.”

Officials stress so far there is no evidence a dangerous substance has been sent. They point out there have been numerous hoax mailings in the years since the 2001 anthrax attacks.

A GOP aide tells NBC News that one of House Speaker John Boehner’s district offices received mail Tuesday containing a powdery substance that proved to be harmless. On Wednesday, Senate staff received a notice warning about suspicious mail.

Senate Sergeant at Arms Terrance Gainer said offices should be on alert because “the author of the letters has indicated that additional letters containing a powdery substance will be arriving at more Senate offices and that some of these letters may contain an actual harmful material.”

Senate staff are being warned to look out for letters postmarked Portland, Ore.

New York authorities, meanwhile, are reaching out to security officials at major media companies.

The FBI in Oregon has been contacted to try to help track whoever sent the threatening mail.

(Source: NBC New York)