The letter was found to contain Ricin.
A letter containing the lethal toxin, ricin, sent to the U.S. President by yet to be identified individuals, has been intercepted.
The letter, which arrived at a facility where it was tested on April 16, is related to another laced with ricin intended for a U.S. senator, the Federal Bureau of Investigation, FBI, said, in a report by the BBC.
The FBI said the letters addressed to the President and Republican Senator Roger Wicker were both postmarked Memphis, Tennessee; and dated April 8.
The contents of the letter intended for President Obama are being sent to an accredited laboratory for further analysis, the FBI said, with results expected in 24 to 48 hours.
The Bureau also said there was no link between the letters and the Boston explosions that killed three people at a Marathon.
Ricin, extracted from castor beans, is 1,000 times more toxic than cyanide. It is one of the waste products of castor oil production. It can be fatal when inhaled, swallowed or injected, although it is possible to recover from exposure.