The Swedish military spent the past three days hunting for a Russian submarine in waters off the coast of Stockholm after they reportedly intercepted a distress signal indicating "foreign underwater activity," but Russian authorities have denied any illegal breach of waters in the Baltic and said none of their subs were in the area.
Swedish intelligence officials first detected an emergency signal Thursday evening. They believe it was emitted from an underwater craft experiencing mechanical problems, according to Swedish media.
Fourteen hours later, a foreign vessel reportedly surfaced amid the scattered islands off the Swedish coastline, setting off a flurry of military activity Friday reminiscent of the Cold War exploits of the '80s, when neutral Sweden would regularly scan the archipelago for Soviet submarines.
Swedish newspaper Svenska Dagbladet reported that the Swedish military intercepted encrypted messages between transmitters situated on the Stockholm archipelago and the Russian exclave of Kaliningrad. The Swedish military has neither confirmed nor denied these reports.
Moscow flatly rebuffed the claims.
"There has been and there are no extraordinary, let alone emergency, situations involving Russian warships," Russian Interfax news agency quoted a spokesman for the Russian Defence Ministry as saying.
A report in Svenska Dagbladet speculated that a damaged submarine may have surfaced to receive help from a support vessel, possibly a Russian oil tanker that was reportedly seen circling the waters off Stockholm.
The tweet below purports to show the October movements of the tanker.
By Sunday, the hunt had grown to a large-scale counter-intelligence operation involving Swedish ships, helicopters, minesweepers, a stealth anti-sub corvette, and 200 troops scouring the area for any sign of the vessel's movements.
The head of the operation for the Swedish military said Friday that there had been no armed intervention, but they were confident about the tipoff and that military activity would continue as long as necessary.
"We still consider the information we received as very trustworthy," Captain Jonas Wikstrom told reporters. "I, as head of operations, have therefore decided to increase the number of units in the area."
The suspicious activity could be the first real test for Swedish Prime Minister Stefan Lofven, whose center-left government came into office mere weeks ago. The activity also comes amid an uptick in recent reports of Russian naval and air activity in the region.
Last week, Finland accused Moscow's navy of interfering with one of its environmental research vessel in international waters, while last month, Sweden protested Russia's "serious violation" of its airspace after it spotted two Russian warplanes flying over its territory.
The massive sweep for the underwater vessel comes in response to fears among Baltic and Nordic states of increased Russian intelligence and military activity in the area, in the wake of the ongoing Ukraine crisis that ignited earlier this year.
Follow Liz Fields on Twitter: @lianzifields