White House Press Secretary Jay Carney has briefed the media, following two suspicious letters addresSed to the President and a US Senator.
He said: "There was a letter addressed to the President at an off-site mail facility. It was noticed to have contained a suspicious substance and tests were undertaken.
"The FBI has the lead in that investigation and has said they will be conducting further tests to determine what the nature of the substance is.
"There was another letter detected by Capitol Police that was sent to a US Senator that is also part of the investigation by the FBI...The President, of course, has been briefed on these letters."
More top news
Eva Echeverria claimed she developed ovarian cancer from using the company's talc products like Baby Powder.
Thousands of gallons of waste, including rotting animal carcasses, are being dumped in the countryside, an investigation has found.
Rain in the north tonight, cloudy and humid in the south