US officials have intercepted an envelope addressed to the White House that contained the poison ricin, a law enforcement official says.
The letter believed to have come from Canada was intercepted at a government facility that screens mail addressed to the White House and President Donald Trump.
A preliminary investigation indicated it tested positive for ricin, a poison found naturally in castor beans, the official says.
Federal investigators were working to determine where the enveloped originated from and who posted it. The FBI, the Secret Service and the US Postal Inspection Service were leading the investigation.
In a statement, the FBI said agents were working to investigate "a suspicious letter received at a US government mail facility" and that there is "no known threat to public safety".
There have been numerous incidents involving envelopes mailed with ricin to US officials.
In 2018, a Utah man, William Clyde Allen III, was indicted for making ricin-related threats, including mailing a threat against Trump and other federal officials including FBI Director Christopher Wray. Allen remains in custody.
In 2014, a Mississippi man was sentenced to 25 years in prison after sending letters dusted with ricin to president Barack Obama and other officials.
Also in 2014, a Texas actor was sentenced to 18 years jail for mailing letters containing ricin to Obama and former New York mayor Michael Bloomberg.
Australian Associated Press