Poison-laced letter to Obama intercepted

Washington, April 17 (IANS) Two days after the deadly Boston marathon bombings, the FBI Wednesday said a letter addressed to President Barack Obama tested positive for the poison ricin.

The letter, intercepted at an off-site White House mail facility, was apparently from the same sender who mailed a "very similar" letter to Republican senator Roger Wicker Tuesday, the FBI said.

The letter is being tested further and results from full laboratory tests are expected in the next 24 to 48 hours, the agency said.

NBC News cited federal officials as saying they believe they know who sent the letters, but no arrest was made because authorities were waiting for further test results.

Ricin is made from castor beans and can kill within 36 hours. There is no antidote. Some threatening letters simply contain ground castor beans, resulting in a positive field test for ricin without the concentrated poison.

Filters at a second government mail screening facility also tested positive for ricin in preliminary screening Wednesday.

NBC News cited an FBI official as saying the agency did not initially believe the letters were related to the attack on the Boston Marathon Monday.

Authorities cleared the atrium of a Senate office building Wednesday and Capitol police were also investigating a suspicious package at the office of Republican senator Richard Shelby. Shelby's staff had not been evacuated.

The Wicker letter was postmarked Memphis, Tennessee, and had no return address. The FBI confirmed the preliminary positive test on it Tuesday.

That letter was intercepted at a postal facility in Maryland that screens mail sent to Congress, and never reached Wicker's office.

Other senators were made aware of the Wicker letter during a briefing Tuesday evening on the bombing in Boston, NBC News said.

Democrat Senator Claire McCaskill told the channel that the person who sent Wicker the letter writes often to elected officials.