The FBI confirmed on Wednesday a suspect has been arrested for mailing letters containing poison ricin to President Barack Obama and two others.

The FBI said in a statement the suspect was identified as Paul Kevin Curtis, who was "believed to be responsible for the mailings of the three letters sent through the U.S. Postal Service which contained a granular substance that preliminarily tested positive for ricin."

The suspect, 45, was arrested at his residence in Corinth, Mississippi following an investigation conducted by the FBI, the Capitol Police, the Postal Inspection Service and the Secret Service.

The letters were also addressed to a U.S. senator, the White House, and a Mississippi justice official.

The FBI confirmed on Wednesday morning a letter addressed to the president has been intercepted and preliminarily tested positive for ricin but the authorities have not found a link to Monday's Boston bombings.

The suspicious letter arrived at the White House off-site mail facility on Tuesday, the same day that another letter addressed to Senator Roger Wicker was intercepted and tested positive for ricin, a highly toxic substance.

The incidents came one day after two explosions occurred near the finish line of the Boston Marathon, killing three people and wounding over 170 others. The authorities called the Boston bombings an "act of terror," but the motives and perpetrators remained unknown.