A package addressed to Donald Trump containing the poison ricin was intercepted, according to reports.
Two tests confirmed the presence of ricin, a highly toxic compound extracted from castor beans that has been used in terror plots, CNN reports.
The report said a package containing ricin was intercepted before reaching the White House earlier this week.
Two law enforcement officials confirmed the report to CNN.
The FBI and Secret Service are investigating but the FBI said that at this time there is no known threat to public safety.
The envelope believed to have come from Canada was intercepted at a government mail centre before it arrived at the White House, the New York Times and Wall Street Journal also reported.
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."
Mirror Online has contacted Donald Trump representatives for comment.