A martial arts instructor from Mississippi has been charged with attempting to use a biological weapon after ricin-laced letters were sent to Barack Obama and other officials.
Senator Roger Wicker in Washington. Credit: AP Photo/J. Scott Applewhite
The US Senate sergeant at arms said in a warning to members of the Senate that all employees should be vigilant in the wake of a poisoned letter sent to a Senator.
Terrance Gaines said in a written statement: "Senate employees should be vigilant in their mail handling processes for ALL mailings."
Members of the Senate were briefed on the ricin incident by Mr Gaines during a meeting with FBI director Robert Mueller and Janet Napolitano, the secretary of Homeland Security, on Tuesday on the bombings in Boston.
The two incidents have not been connected.
Several senators told reporters after the briefing that the incident reminded them of the anthrax attacks in the wake of the 9/11 attacks on the Pentagon and World Trade Center.
Several senators said that all mail to the US Senate had been stopped and post offices at the Capitol had been closed as a precaution.
They said they were getting in touch with their state offices, where mail is not routinely screened, to ensure that precautions were being put in place.
The US Senate mail facility has been closed for the next two to three days following the receipt of a letter that tested positive for the poison ricin, the Senate Sergeant at Arms told Reuters.
The envelope was postmarked from Memphis, Tennessee, had no return address, and was not "outwardly suspicious" the Senate sergeant said.
The FBI, US Capitol Police, and other agencies are involved in the investigation of mail testing positive for ricin, he added.
An envelope sent to Republican Senator Roger Wicker of Mississippi tested positive for ricin, Senator Dick Durbin told reporters after a group of lawmakers were briefed by the FBI.
Ricin is a lethal poison found naturally in castor beans.
A spokeswoman for Mr Wicker referred inquiries to US Capitol Police, according to Reuters.
A spokesman for Capitol Police could not immediately be reached for comment.
