Police cordon off front of the White House
Police cordon off front of the White HouseAFP photo

A suspicious letter addressed to the White House and "similar" to one sent to New York Mayor Michael Bloomberg that tested positive for ricin has been intercepted, the Secret Service said on Thursday.

"The White House mail screening facility intercepted a letter addressed to the White House that were similar to letters previously addressed to Mayor Bloomberg in New York," Secret Service spokesman Edwin Donovan said, according to AFP.

"This letter has been turned over to the FBI Joint Terrorism Task Force for testing and investigation," Donovan said in a short statement sent to the news agency.

Two letters sent last week -- one to Bloomberg and one to an official with the gun laws group he helped found, Mayors Against Illegal Guns -- appeared to be laced with ricin, according to preliminary tests, New York police said.

In April, a letter addressed to U.S. President Barack Obama tested positive for ricin. Another letter mailed to Republican Senator Roger Wicker also tested positive for the deadly poison.

A 45-year-old man was later arrested and charged with threatening the life of the president. However, the charges against him were later dropped and another suspect, a rival of the first suspect, was arrested.

The ricin envelopes were sent shortly after the blasts at the Boston Marathon which killed three people, but the FBI said there was no evidence of a connection between the Boston terror attack and the poisoned envelopes.