Washington - Three members of the US Congress have received threatening mail containing a suspicious powder later found to be harmless and law enforcement officials on Wednesday warned that more may be coming.
Another US law enforcement official said letters sent to television personalities Jon Stewart and Stephen Colbert threatened biological attacks on US senators.
Other letters to a number of news organisations and postmarked Oregon warned that 100 letters had been sent to the Washington or home-state offices of US senators and that 10 of those contained a deadly pathogen, a law enforcement source said.
At least two of the letters already received - one to the home-state office of a senator and the other to the district office of a member of the House of Representatives - contained a powdery substance.
Tests found the substance to be harmless, according to a statement by Senate Sergeant at Arms Terrance Gainer, the chamber's chief law enforcement officer.
In a statement to members of the Senate, Gainer did not say what was found in the third letter.
Gainer's notice, “Urgent: Suspicious Mail Alert”, warned that the unidentified sender of the letters “indicated that additional letters containing a powdery substance will be arriving at more Senate offices and that some of these letters may contain actual harmful material”.
He warned that special attention should be paid to letters postmarked from Portland, Oregon.
The official, speaking on condition of anonymity, said the messages to Stewart and Colbert threatened to send letters to all 100 US 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.
The New York Police Department was made aware of the letters received by some news organisations on Tuesday night and alerted the FBI and the US Capitol Police, a law enforcement source said. The letters to the news organisations did not contain any suspicious substances.
The letters demanded an end to corporate money and lobbying in US politics, an end to corporate personhood and called for a new constitutional convention, the source said. The letters were signed “the MIB”.
Organisations and television shows that received the letters were The Daily Show with Jon Stewart, The Colbert Report, Washington Post, the New York Times, USA Today, NPR, the Chicago Tribune, the Los Angeles Times, the Seattle Post-Intelligencer, MacNeil/Lehrer Productions, This Week with Christiane Amanpour, Countdown with Keith Olbermann and Fox News.
“We've responded to several suspicious powder letters in Manhattan. The investigation is ongoing. Preliminary results indicate the powder is harmless,” said New York FBI spokesperson Peter Donald. - Reuters