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In a significant development in the Baltic Sea region, Swedish authorities have intercepted a Russian ship, previously linked to arms transportation, near their western coast. The incident marks the latest in a series of maritime encounters between NATO member states and Russian vessels.

The vessel, named Adler, is a roll-on, roll-off freighter that analysts have identified as having a history of transporting weapons. On Saturday, the ship experienced engine failure and came to a halt within Swedish territorial waters. In response, customs officers and border officials boarded the vessel overnight from Saturday into Sunday.

According to Sweden’s customs service, the crew was cooperative, and the inspection was still ongoing as of Sunday morning. Local reports suggest that Sweden’s intelligence services and prosecutors are also participating in the investigation.

This incident highlights growing concerns among NATO countries neighboring the Baltic Sea regarding Russia’s use of a so-called shadow fleet. These vessels are reportedly employed to bypass Western sanctions on oil and to ferry weapons.

The Adler had previously been stopped by a NATO country when Greek authorities boarded it in 2021 to verify it wasn’t transporting weapons to Libya, an action that drew the ire of Moscow.

The vessel is owned by M Leasing LLC, which is sanctioned by the US, EU and multiple European countries for its role in transporting North Korean ammunition for use in Russia’s war against Ukraine.

It issued a distress call on Saturday morning near the Swedish town of Höganäs, in the straits between Denmark and Sweden.

The boarding by Swedish officials comes after a number of vessels belonging to Russia’s shadow fleet cut cables and pipelines in the Baltic Sea in 2024, culminating in Finnish border guards abseiling on to the Eagle S oil tanker on Boxing Day last year to detain its crew.

Finland brought a case against the captain and senior officers of the Eagle S for gross sabotage as it found that the cables cut by the ship were in international waters. The case was later dismissed by a court in Helsinki, which ruled the country lacked jurisdiction, highlighting the difficulties of holding those accused of sabotage and hybrid attacks accountable.

Asked by the Financial Times if that gave Russian-backed vessels carte blanche in international waters, Finland’s foreign minister Elina Valtonen said in October: “Yes, and that’s a problem.”

But Valtonen and officials from other Baltic Sea countries also hailed the impact of Nato’s increased presence in the area, which has seemingly acted as a deterrent for further serious acts of sabotage this year.

However, ministers across the region are still on high alert, especially due to the risk of an environmental catastrophe in the shallow and narrow Baltic Sea due to Russia’s use of old vessels.

Lady Mariia, another Russian roll-on roll-off vessel that has been used to transport weapons, also developed engine trouble off the coast of Sweden earlier this month, but regained control within a few hours.

Finland’s Prime Minister Petteri Orpo told the FT this week: “We have to find the tools to protect our critical infrastructure that is situated in international waters. It is not OK that someone is on purpose destroying our property.”

This story has been updated to make clear that the case Finland brought against the captain and senior officers of the Eagle S was later dismissed.