"The White House mail screening facility intercepted a letter addressed to the White House that were similar to letters previously addressed to Mayor (Michael) Bloomberg in New York," reported Xinhua citing Secret Service spokesperson Edwin Donovan.
"This letter has been turned over to the FBI Joint Terrorism Task Force for testing and investigation," Donovan said in a statement.
According to federal law enforcement officials, the letter was being tested for ricin. It was received Thursday at an off-site facility, but it did not reach the White House.
If confirmed, this would be the second letter addressed to US President Barack Obama that was laced with ricin in recent months.
Last month, a Mississippi man was arrested for trying to send ricin-laced letters to Obama, a US senator and a local official.
Authorities said Wednesday that threatening letters addressed to New York mayor in both -- New York and Washington D.C. -- have been found containing ricin.
A letter addressed to the mayor arrived late last week at a municipal building in New York, and a second letter containing the poison arrived at a building in Washington that houses Mayors Against Illegal Guns, a group Mayor Bloomberg helps run and finances.
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