Emergency services have been called to the State Department in Washington for the second time in three days after a white powder was found.
Officials were briefing journalists when an announcement about the latest incident came on the speakers. The FBI is now investigating.
Spokesman Mr Richard Boucher said: "We found another white powdery substance in a correspondence office and the FBI, the fire department and the hazardous materials unit have been called in."
Another announcement then said: "The area of concern has been completely contained at this time. There is no need for alarm."
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On Wednesday a white powder was found on a mailroom floor on the sixth floor.
Mr Boucher said it posed no danger but it's still being tested.
PA