Police have launched an investigation after several foreign embassies in Moscow received envelopes containing a mysterious white powder.

At least three embassies belonging to European and Middle Eastern countries have received the envelopes, the Interfax news agency cited an unnamed source as saying Wednesday.

In an email to The Moscow Times the Dutch Embassy confirmed it was among the embassies but said work continued as normal. “Like many other embassies we have received an unknown substance,” the statement said. “It was checked by [the] appropriate Russian services and found not harmful.”