A parcel containing suspicious powder-packed envelopes received at a Boeing mail room near Seattle on Saturday morning was posted in Ireland, according to local reports.
Preliminary laboratory tests done on the substances by the Seattle Fire Department have found no traces of anthrax or any other biological agents.
The parcel was received at a Boeing plant in the town of Kent, Washington State, and, according to the local fire department, the address on the package was handwritten and "addressed to no one in particular".
Speaking to local media organisation, KOMO 4 News, Mr Terry McCartin of the Kent Fire Department said the parcel "had a couple of stamps indicating that it came from Ireland".
After a mail room employee opened the parcel and grew suspicious, the fire department's hazardous materials team was called in. "There was a white envelope opened by an employee here at Boeing out of which came a white powdery substance," Mr McCartin said.
But early results were negative for anthrax and later testing at the State Public Health Lab in Shoreline also proved negative.