Officials intercepted Thursday a letter addressed to the White House that was similar to threatening letters sent to New York Mayor Michael Bloomberg and a group he founded.
The off-site facility that screens mail addressed to the White House turned the letter over to the FBI Joint Terrorism Task Force for testing and investigation, U.S. Secret Service spokesman Brian Leary said.
A U.S. law enforcement official said the letter was addressed to President Obama.
The letters sent to Bloomberg and his group are suspected of containing poison. Preliminary tests indicate ricin was found in the letters, New York Deputy Police Commissioner Paul Browne said Wednesday.
Officials have not said whether any such substance was found in the letter sent to the White House.
The law enforcement official did not know the status of testing on anything found in the letter and did not disclose whether there was a message. But the source said the letter appears similar to the notes sent to Bloomberg and Mayors Against Illegal Guns.