The letter comes a day after lawmakers said a letter was mailed to Sen. Roger Wicker that tested positive for poisonous ricin.
Update, 4/17/13, 7:15 p.m. MISSISSIPPI --A man in Mississippi has been arrested and accused of sending letters with suspected ricin poison to President Barack Obama and other leaders.
FBI Special Agent in Charge Daniel McMullen said the man was arrested Wednesday. His name wasn't immediately released publicly.
Authorities still waited for definitive tests on the letters to Obama and Sen. Roger Wicker, R-Miss., which had raised concern Wednesday at a time when many people were jittery after the Boston bombings.
An FBI intelligence bulletin obtained by The Associated Press said those two letters were postmarked Memphis, Tenn.
The FBI says preliminary tests on a letter sent to President Barack Obama indicate the presence of poisonous ricin.
The letter is undergoing further testing because preliminary field tests can be unreliable, creating false positives.
The letter was intercepted at a facility away from the White House. It comes the day after officials said a letter sent to Sen. Roger Wicker tested positive for poisonous ricin. That letter to Wicker, a Republican, was intercepted at a Senate mail facility just outside Washington.
The FBI says there is no indication of a connection to the bombing at Monday's Boston Marathon.