A letter addressed to President Donald Trump that was intercepted before it reached the White House tested positive for the deadly poison ricin earlier this week, law enforcement officials said.
The Federal Bureau of Investigations said Saturday afternoon they are investigating "a suspicious letter received at a U.S. government mail facility" alongside its partners at the U.S. Secret Service and the U.S. Postal Inspection Service.
Law enforcement officials said a letter was detected at an off-site facility that screens mail addressed to the White House.
"At this time, there is no known threat to public safety," the FBI said in a statement.
Related: President Trump holds a rally in North Carolina
One official said the letter tested positive to ricin in both a field test and a subsequent laboratory test.
A second official said the FBI, Secret Service and the Postal Inspection Service are trying to determine where the letter came from. It’s unclear when the letter was intercepted.
Other letters that have also tested positive for ricin were discovered in different facilities, an official said. While it is unclear how many additional poisoned letters were found, most of them seem to be addressed to prisons. Only one was apparently addressed to a political figure, the official said.
The White House and Secret Service did not immediately return a request for comment.
Ricin is highly toxic that could cause nausea, vomiting, and internal bleeding of the stomach and intestines. Depending on the severity of the exposure, it can also cause failure of the liver, spleen and kidneys, and death by the collapse of the circulatory system.