A senior law enforcement official revealed to the American partner of the BBC, CBS News, that the substance was found in a storage facility that White House staff and guests routinely use to store their mobile phones.
At 20:45 local time (00:45 GMT) on Sunday, it was discovered, and the White House complex was immediately shut down out of an abundance of caution.
The West Wing, a vast, multi-level portion of the White House that contains the president of the United States' offices, is where the Oval Office and the Situation Room are situated.