Another letter sent to Barack Obama is subject to testing for the deadly toxin ricin, the US secret service has revealed.
Similar letters have also been forwarded to the address of New York Mayor Michael Bloomberg.
The note addressed to the President was intercepted by a specialist screening facility at the White House.
It has been turned over to the FBI’s Joint Terrorism Task Force for testing and investigation.
Officials have said that two threatening letters postmarked in the southern state of Louisiana and containing traces of the deadly poison ricin were sent to Mayor Bloomberg in New York and to his gun-control group in Washington.
On April 18th, a Mississippi man was arrested for trying to send ricin-laced letters to Obama, a senator and a judge.