An envelope posted to the White House containing the lethal substance ricin was intercepted by US authorities on Saturday.
The letter addressed to President Donald Trump appears to have been sent from Canada, and officials have identified a woman as a suspect, according to a report by the New York Times.
It was stopped at the final off-site government mail center before it arrived at the White House.
“The FBI and our US Secret Service and US Postal Inspection Service partners are investigating a suspicious letter received at a US government mail facility,” the FBI said in a statement, according to Times. “At this time, there is no known threat to public safety.”