The press conference was held in Berga on a rainy and grey day by the water.
The communications director of the Armed Forces, Erik Lagersten, told reporters that "the operation was going into a new phase".
When pressed to explain what he meant, Lagersten was extremely delicate with his choice of words, saying that the hunt was so far being carried out "according to plan".
Many journalists were left baffled after the mysterious "new phase". Photo: TT
He refused to confirm or deny a series of questions from journalists on the scene.
"I cannot comment on an ongoing operation," he repeated.
Johanne Hildebrandt, a fellow at The Royal Swedish Academy of War Sciences, told The Local that the choice of words suggested the Armed Forces were toning down operations.
"I think they're stepping down but they don't want to say it," she said, adding that the real question was why the public doesn't know more about the other times submarines have violated Swedish territory.
The search has reached the sixth day. Photo: TT
Search teams resumed their large-scale hunt for the suspected submarine on Wednesday morning after spending the night watching and listening to other ships and vessels in the area.
A few hours ahead of the briefing, officer Dag Enander told news agency TT that there were no plans to downsize the operation in the Baltic Sea:
"We are moving forward with the same scale and orientation. We'll drive on as before, business as usual".
Battleships, minesweepers, helicopters and more than 200 troops have been scouring an area about 30 to 60 kilometres from the Swedish capital after a "man-made" object was spotted.
But some defence experts have cast doubt on the chances of a quick discovery.
Jörgen Elfving, a former lieutenant colonel and military expert, told Swedish network SVT:
"This is an operation that takes time. It needs patience".
He added: "What is going on is like looking for a needle in a haystack".
But Deputy Operation Commander Anders Grenstad insisted that the Swedish military had time on its side.
"We can keep going for a long while if we so desire," he told SVT.
The military is six days into its search. Photo: TT
Speaking at a press conference on Tuesday, Supreme Commander General Sverker Göranson said that the most important goal of the operation was to "send a very clear signal that Sweden and its armed forces are acting and are ready to act when we think this kind of activity is violating our borders."
"Our aim now is to force whatever it is up to the surface… with armed force, if necessary," he added.
He added that submarines are "extremely difficult" to find, and that Sweden has never succeeded in the past when it came to tracking them down.
"And no one else has either," he added.
During more than a decade of hunting Russian U-boats in the 1980s and early nineties, Sweden never succeeded in capturing one, except in 1981 when the U137 ran aground several miles from one of Sweden's largest naval bases, triggering an embarrassing diplomatic stand-off for Russia.
Göranson said there had been more than 100 reported sightings of a suspect vessel from members of the public in the past day or so.
"We're still getting more reports, and I want to underline the fact that we're happy about this," Göranson added.
"You mustn't forget that there's a great deal of work to be done with such a flood of reports. We have to analyze and confirm them all."Sweden's military has now been out on the hunt for six days, with the operation moving "across the archipelago" on Tuesday.
Jesper Tengroth, press officer for the Swedish military, told The Local that the focus had switched from just the southern islands on Monday.
Sweden's military is out searching for the suspect vessel. Photo: TT
Out in the Stockholm archipelago, The Local met Bosse Linden, a 54-year-old water taxi driver from Vaxholm who also served in the Swedish navy for 25 years.
"Things like this have happened before but I am not so scared. I think there is something out there, but the archipelago is really big," he said.
He believes that Russia could be "playing a game of hide and seek" or simply making use of the broad stretch of "special water" which he describes as a dream location for people who want to learn how to drive boats or navigate submarines.
"If you learn how to navigate a submarine here then you will be the best," he told The Local.
"I don’t think it is a war mission. I don't think someone is going to take over. But some people are scared," he added.
In another development, Sweden's Prime Minister Stefan Löfven said on Thursday that his government planned to increase spending on defence.
"We agree on a broad basis between many parties in Sweden in the Swedish parliament that we need to increase our capacity, meaning that we need to put more resources into defence," he said on a visit to the Estonian capital Tallinn.