Police and rescue services outside an office that received a letter containing the powder. Photo: P4 Göteborg

Swedish police are to investigate the wave of letters containing white powder sent to companies and government authorities over the past week.

They are still waiting for the final laboratory test results of the powder, but say they cannot rule out the possibility that the envelopes may be linked.

The envelopes have been sent to addresses in Stockholm, Umeå, Gällivare, Malmö and Helsingborg and anyone that has come in contact with the powder has since been decontaminated and offered medical care.

"Until we know what...