Police have ordered some fifty people not to leave a building in Gällivare, 1,100km north of Stockholm, after a woman working for a housing company came into contact with a white powder when opening the day's post.
"She was told to stay with the envelope behind a shut door, then police wanted to extend the cordon to the entire building," the head of the company, Esa Norajävrvi, told news agency TT.
Police have sent the powder for analysis and expect to have preliminary results by 5.30pm.
Another envelope containing an unidentified substance leaked at a postal terminal in Umeå on Monday morning, police said.
Police cordoned off the postal terminal and the adjoining car park in the Teg district by the city's airport as a precaution.
“We received information this morning from the postal terminal in Umeå about an envelope containing white powder,” spokesman Peder Jonsson told TT.
“At around the same time information came in about similar envelopes at Handelsbanken in Gällivare, while a number of other business and organizations have subsequently received envelopes of a similar nature.”
Police said the powder would be sent for analysis.
Maria Ibsén, a spokeswoman for postal company Postnord, confirmed that staff at the terminal in Umeå had alerted the police to the suspicious substance after it leaked from an envelope on Monday morning.
Postnord said some 10,000 households in Holmsund, Obbola, Sörmjöle, Ersboda and Ålidhem would not receive any post on Monday as a result of the mystery find.
On Wednesday, police in Stockholm were called to government offices after staff opened an envelope containing white powder.
Two days earlier, a similar delivery was sent to the Swedish Tax Agency’s office in Malmö.