An envelope addressed to the White House and intercepted by U.S. authorities contained a substance identified as ricin, a deadly poison that appeared to have been sent from Canada, the Royal Canadian Mounted Police (RCMP) said.

Royal Canadian Mounted Police spokesman confirmed it received a request for assistance from FBI in connection with a suspicious letter sent to the White House.

Asked about the reports, the FBI said the agency and “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.”