WASHINGTON (AP) — The Secret Service said Thursday that a suspicious letter addressed to President Barack Obama and similar to ricin-laced ones sent to New York Mayor Michael Bloomberg has been intercepted by a White House mail screening facility.

The letter has been turned over to the FBI's Joint Terrorism Task Force for testing and investigation.

It was unclear precisely how the letter, which was intercepted Wednesday by the White House facility, was similar to letters laced with the poison ricin and addressed to Bloomberg. The screening facility is located away from the White House complex.

White House spokesman Josh Earnest said Thursday that Obama was aware of the letter addressed to him.

Two threatening letters postmarked in Louisiana and containing traces of the deadly poison ricin were sent to Bloomberg in New York and to his gun-control group in Washington, officials said.

The anonymous letters were opened in New York last Friday at the city's mail facility in Manhattan and in Washington on Sunday at an office used by Mayors Against Illegal Guns, the nonprofit started by Bloomberg, police said Wednesday.

Police said preliminary testing indicated the presence of ricin in both letters involving Bloomberg, but that more testing would be done. Police said the threats contained references to the debate on gun laws and an oily pinkish-orange substance.

Last month, authorities in Washington intercepted a letter addressed to Obama that was found after testing to contain ricin. The letter was similar to one mailed to Mississippi Republican Sen. Roger Wicker, which also tested positive for ricin.

Federal authorities last month arrested a Mississippi man suspected of sending the ricin-laced letters to Obama, Wicker and a Mississippi judge.