"The Swedes are for the first time, seriously scared. Frightened of Russia, of what they are up to," said Wallström in an interview in the Svenska Dagbladet daily on Saturday.
While Wallström argued that Sweden was "peace-loving", the country demanded respect.
"No one should be in any doubt that we demand respect. We are ready to act to protect our nonalignment and our borders."
Wallström's words come a day after the Swedish military claimed that it had 'conclusive proof' that there was a foreign vessel in Sweden's waters last month.
A sonar image showing sub-sea tracks left behind by a mini-submarine: Photo: Swedish Armed Forces
Speaking at a packed press conference on Friday, Supreme Commander of the Swedish Armed Forces Sverker Göransson revealed that a foreign vessel was in Stockholm's archipelago in October.
But he said the Swedish military had been unable to determine which country it came from.
"We have confirmation that there has been a small submarine in the archipelago," he told reporters.
Prime Minister Stefan Löfven added: "We will defend our territorial integrity using all means at our disposal."
While suspicion has fallen on Russia, its defence ministry has denied any of its ships were involved in the incident.