POLISH Prime Minister Donald Tusk accused Russia of using dark fleet* tankers to damage undersea infrastructure, following another flashpoint in the Baltic Sea yesterday.

Tusk said threats to undersea cables “are not abstract” and claimed “units from the shadow fleet primarily come from Russia, even if they sail under other flags” at a briefing with navy personnel and media in Gdynia today.

The prime minister’s comments come following another flashpoint in the Baltic Sea, when a dark fleet tanker “performed suspicious manoeuvres near the power cable connecting Poland and Sweden”, Tusk said on X.

Vice-admiral Krzysztof Jaworski told Reuters the vessel in question was Antigua-flagged, 2005-built suezmax Sun (IMO: 9293117), which was sanctioned by the EU just this week.

Sun entered the Kattegat between Denmark and Sweden on May 15, before heading Denmark’s Great Belt and into the Baltic Sea.

Between May 16 and May 20, Sun performed manoeuvres back and forth over the same small area, which Tusk named “suspicious”. The undersea SwePol cable, which connects Poland and Sweden, also runs in that same region.

The prime minister said a patrol flight was sent to the scene, after which Sun departed the area on May 20. It is now at anchor in the Gulf of Finland.

Tusk said investigations into whether any explosives were planted were ongoing. No damage to the cable has been reported as of yet.

A spokesperson for the Swedish armed forces said Nato units identified a vessel in the Baltic Sea on May 20  that “manoeuvred/navigated in a suspicious manner in proximity of critical undersea infrastructure”.

“Swedish units were not directly involved but we have a good overview of the area and as always we co-operate with our allies. The vessel in question has left the area.”

Lloyd’s List Intelligence ship-tracking manager Richard Smale, who also served as a deck officer with Maersk Line and shipmanager for CMA CGM, said the route taken by the tanker Sun appeared “highly irregular” based on tracking data from Lloyd’s List Intelligence’s AIS network.

“Tankers of this type normally adhere to established navigation routes through the Baltic Sea, both for navigational efficiency and safety,” he said.

“To see a vessel of this class divert from those lanes is not consistent with routine commercial practice.”

Smale stressed he was not attributing motive, but said the vessel’s track raised legitimate questions. “There is no operational justification, in standard tanker navigation, for loitering or conducting erratic manoeuvres in that specific area. From a professional maritime perspective, the behaviour is not just unusual; it’s highly concerning.”

He added that the outcome of the investigation would be closely watched, particularly given the wider pattern of merchant vessels exhibiting similar erratic behaviour in the Baltic Sea in recent months. “This isn’t occurring in isolation. There’s a broader context of unusual maritime activity in the region that cannot be ignored.”

The most high-profile case involved dark fleet tanker Eagle S (IMO: 9329760), which was accused of damaging the Estlink 2 cable off Finland on December 25, 2024.

A Russian fighter entered Estonian airspace just last week after Estonian forces sought to escort sanctioned tanker Jaguar (IMO: 9293002) out of its waters, prompting Nato jets to be scrambled.

Tusk was unequivocal in his assessment of the situation in the Baltic.

“There is no point in building some illusion, there is no point in denying these facts. The Baltic Sea may become a place, like Poland’s eastern border today, of permanent confrontation, a hybrid one,” he told reporters in Gdynia.

“Although it is no longer entirely hybrid. If someone sends units to destroy infrastructure, then I don’t know why we should call it a conflict or a hybrid war.”