The U.S.  Secret Service has intercepted a letter addressed to President Barack Obama that contained  what’s described as a suspicious substance.

The FBI said a preliminary test showed evidence of Ricin, but warned only a full-scale second test can conclude if the letter was indeed laced with poison.

The letter was caught at an off-site sorting plant on Tuesday.

The FBI also said filters at a second government mail screening facility preliminarily tested positive for Ricin Wednesday morning, and that mail is being tested.

The FBI says there is no indication of a connection to the attack in Boston.