FBI probes origins of letter to Obama containing "suspicious" substance

WASHINGTON (AFP) - A letter addressed to President Barack Obama containing a "suspicious" substance was intercepted at a mail screening facility outside the White House, the United States Secret Service said on Wednesday.

The letter was discovered at the remote facility which is used to screen White House mail on Tuesday, the same day authorities said a letter was sent to Senator Roger Wicker which was laced with ricin, a deadly poison.

Secret Service spokesman Edwin Donovan said the agency, which protects the president and his family, was working closely with the US Capitol Police and the Federal Bureau of Investigation to trace the origins of the letter.

At the Capitol, sections of two Senate office buildings were cordoned off amid reports of a suspicious package.

Upon exiting one of the buildings, Senator Ron Wyden said: "Apparently there was a package over there." US Capitol Police confirmed a man was being questioned.

"Right now they are interviewing a person but that person is not in custody. He has not been detained," a US Capitol Police officer told AFP.

The discovery of the letters rattled nerves following the bomb attacks near the finish line at the Boston Marathon on Monday which killed three people and injured more than 180 others, though it was not clear if the incidents were linked.

The episodes also recalled the mysterious series of letters laced with anthrax that were sent to lawmakers and some journalists following the September 11 attacks in 2001 which killed five people and sickened 17 others.