According to reports, an envelope addressed to the White House which contained ricin poison was intercepted on Saturday.
Officials told The New York Times that the envelope probably originated in Canada.
The letter was discovered at an official facility that screens mail addressed to the White House.
The FBI wrote on its official Twitter account: The FBI and our U.S. Secret Service and U.S. Postal Inspection Service partners are investigating a suspicious letter received at a U.S. government mail facility. At this time, there is no known threat to public safety.