The US Secret Service has said that it has discovered a letter addressed to President Barack Obama containing a suspicious substance. Preliminary tests appeared to show the envelope contained the poison ricin.
The letter was intercepted at a mail screening facility located away from the White House, the US Secret Service said Wednesday.
The suspicious correspondence had been found on Tuesday, the same day that a letter was sent to Mississippi Senator Roger Wicker. That letter was found to contain the deadly poison ricin.
Secret Service spokesman Edwin Donovan said the agency was trying to trace the origins of the letter along with the assistance of the US Capitol Police and the Federal Bureau of Investigation (FBI). The Secret Service is responsible for the security of the president and his family.
"This facility routinely identifies letters or parcels that require secondary screening or scientific testing before delivery," Donovan said.
The FBI said that preliminary field tests indicate presence of ricin, although further testing was needed for confirmation. "Only a full analysis performed at an accredited laboratory can determine the presence of a biological agent such as ricin," said an FBI statement. "Those tests are currently being conducted and generally take 24 to 48 hours."
Tensions have been high across the US since the bombings on Monday at the Boston Marathon, when three people were killed and more than 170 injured. The FBI on Wednesday said there were no indications of a link between the letters and the bombing.
All mail to the US Senate has reportedly now been stopped and the Senate mail facility closed while the investigation is underway. Congressional mail has been screened off-site since letters laced with anthrax were sent to Capitol Hill in the wake of the Sept. 11, 2001, attacks on the Pentagon and World Trade Center.
Ricin can prove lethal, even in small quantities, when ingested orally. The poison, found naturally in castor beans, can cause respiratory problems when inhaled.
rc/ipj (AP, Reuters, AFP)