The US Secret Service said on Wednesday that a letter addressed to President Obama, containing a suspicious substance, was intercepted at a screening facility outside the White House.

The letter was received on Tuesday — similar timing to a letter addressed to Senator Roger Wicker, Republican of Mississippi that tested positive for Ricin. The letter had similar markings and was similar in appearance to the one addressed to Mr. Wicker, according to a law enforcement official.

The Secret Service did not disclose what was in the letter or provide any details, saying it was intercepted in a facility that “routinely identifies letters or parcels that require secondary screening or scientific testing before delivery.”

An official said the Secret Service was working with the Capitol Police and the Federal Bureau of Investigation.