According to a U.S. law enforcement official, federal authorities have intercepted a poisonous envelope that contained ricin and was on its way to the White House.
The FBI assisted the Royal Canadian Mounted Police in the operation. The preliminary investigation determined the letter originated in Canada and federal detectives are working to identify its exact sender.
The suspicious letter was intercepted at a government department that checks the mail addressed to the White House.
The ongoing investigation cannot be publicly discussed, according to the source that asked for anonymity.
It was confirmed, however, that the mail tested positive for ricin, a natural poison that can be found in castor beans.
There was no immediate threat to public safety in connection with the incident, the official insisted.