TORONTO -- An envelope addressed to the White House that contained the poison ricin may have come from Canada, investigators say, and the RCMP has been called in to investigate.

Officials intercepted the letter at a U.S. government facility that screens mail before it reached U.S. President Donald Trump. Investigators are now working to track down its source.

“Initial information from the investigation suggests that the letter originated in Canada,” RCMP spokesman Dan Brien said in a statement.

The RCMP is now working with the FBI on the investigation. Officials have not indicated where in Canada the package may have originated.

Minister of Public Safety Bill Blair acknowledged the incident in a statement to CTV News.

“We are aware of the concerning reports of packages containing ricin directed toward US federal government sites. Canadian law enforcement is working closely with their US counterparts. As this is an active investigation we cannot comment further,” Blair’s office said in a statement Saturday.

In a statement, the FBI said agents were working to investigate "a suspicious letter received at a U.S. government mail facility" and that there is "no known threat to public safety.”

With files from The Associated Press