1 of 2
Associated Press
In this courtroom sketch, Manssor Arbabsiar, center, reads a statement Thursday, May 30, 2013, in Manhattan Federal Court, in New York before the judge sentenced the former used car salesman from Corpus Christi, Texas, to 25 years in prison in a failed conspiracy to kill the Saudi Arabian ambassador to the United States by bombing a Washington restaurant. (AP Photo/Elizabeth Williams)

WASHINGTON — A suspicious letter mailed to the White House was similar to two threatening, poison-laced letters on the gun law debate sent to New York Mayor Michael Bloomberg, one of the nation's most potent gun-control advocates, officials said Thursday.

The Secret Service said the letter was addressed to President Barack Obama and was intercepted by a White House mail screening facility. Two similar letters postmarked in Louisiana and sent to Bloomberg in New York and his gun control group in Washington contained traces of the deadly poison ricin.

It wasn't immediately clear whether the letter sent to Obama contained ricin. It was turned over to the FBI's Joint Terrorism Task Force for testing and investigation.

Comment on this story

The two Bloomberg letters, opened Friday in New York and Sunday in Washington, contained an oily pinkish-orange substance.

New York Police Department Commissioner Raymond Kelly said Thursday that all three letters apparently came from the same machine or computer and may be identical but referred specific questions to the FBI.

The FBI said in a statement that field tests on the letters were consistent with the presence of a biological agent, and the letters were turned over to an accredited laboratory for the kind of thorough analysis that is needed to verify a tentative finding.