The United States embassy in Bern was one of 15 diplomatic missions around the world that received envelopes containing white powder, officials said on Wednesday.
The substance was proven harmless in initial tests, US authorities said, but a spokeswoman for the embassy in the Swiss capital said the outcome of further tests was still pending.
Suspicious envelopes were mailed to US embassies including those in Brussels, Berlin, Rome, Bucharest, Rome, Dublin, Oslo and Riga, the Latvian capital.
Officials in Madrid said the substance found in that embassy's envelope was flour. The outcome of a test on the envelope sent to the embassy in The Hague is still pending.
All of the packages were mailed from Texas, authorities said.
Earlier in 2008, the United States moved its offices in Bern to a larger, more secure facility.
In 2001, letters containing the anthrax pathogen killed five people in the US.