WASHINGTON -- A suspicious letter addressed to the White House that is similar to the ones sent to New York Mayor Michael Bloomberg has been intercepted at a mail screening facility, the U.S. 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.

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

Federal law enforcement officials said the letter is being tested for ricin. It was received Thursday at an off-site facility, and did not reach the White House.

If confirmed, this would be the second letter addressed to 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 U.S. senator and a local official.

Authorities said Wednesday that threatening letters addressed to Bloomberg in both New York and Washington, D.C. have been found containing ricin.

A letter addressed to Bloomberg 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 Bloomberg helps run and finances.