Michigan Sen. Carl Levin says authorities are testing a suspicious letter sent to his regional office in Saginaw.
Levin says in a statement that an aide received the letter Wednesday but did not open it. Authorities are investigating and Levin doesn't expect preliminary results of tests until late Wednesday or Thursday.
The Democratic lawmaker says he doesn't know if the mail presented a threat. The staffer who discovered the letter is being kept overnight at a hospital for precautionary reasons but has no symptoms.
Separately, the FBI says a substance in letters sent to President Barack Obama and Mississippi Sen. Roger Wicker have preliminarily tested positive for ricin, a potentially fatal poison. Both letters were intercepted at off-site mail facilities.