Several Russian military ships were observed close to the Nord Stream pipelines in the days before the gas links between Russia and Europe were blown up last year.
A Russian tugboat SB-123 capable of launching and rescuing mini-submarines was seen near the pipelines on September 21 and 22, shortly before the explosions on September 26, according to an investigation by four Nordic state broadcasters based on intercepted radio messages.
Denmark’s overall military command authority confirmed to the Financial Times that it had taken 26 pictures of the special Russian ship SS-750, which had a rescue mini-submarine on board, on September 22 to the east of the Danish island of Bornholm, close to where the sabotage of the twin pipelines took place.
Investigators in Denmark, Sweden and Germany as well as western intelligence agencies are still trying to establish who was behind the pipeline attacks.
In the aftermath, countries such as Norway and Denmark as well as the Nato military alliance have stepped up patrols around critical energy infrastructure, including North Sea oil and gas platforms and thousands of kilometres of pipes and cables.
There has been a drip feed of sightings and supposed intelligence in recent months but no hard evidence as to who committed the sabotage and few official statements from investigators.
Media reports in March suggested a pro-Ukraine group could have carried out the attack but multiple European ministers and the head of Nato urged caution against such speculation, while Kyiv denied the allegations. Russia in turn blamed a “special state service” for the attacks and gave short shrift to the idea that a pro-Ukraine group could be responsible.
Intelligence sources have said that the scale and complexity of the attacks — involving more than 100kg of explosives — pointed to the likelihood of a state actor being behind them.
The SS-750 vessel was first named by German website T-Online and the open source intelligence analyst Oliver Alexander as being one of six Russian ships that appeared to divert from an exercise in the Baltic Sea to sail close to the sabotage site.
A Danish patrol boat P524 Nymfen left harbour on the evening of September 21 and reached the sabotage site the next morning, according to Alexander, four days before the explosions. It is this patrol boat that took the pictures of the SS-750, according to the Danish newspaper Information, which first reported it.
A joint investigation by Nordic state broadcasters NRK, SVT, DR and Yle found evidence of three Russian ships sailing close to the pipelines in June and September: the SB-123 tugboat, the Sibiryakov research ship and a third unidentified vessel. Evidence came from radio messages supposedly from the boats as well as satellite data.
Dmitry Peskov, spokesperson of President Vladimir Putin, told reporters on Tuesday that Russia wanted western countries to publish the evidence.
“The investigation of this terrorist attack should be transparent for everyone and it should be sped up. The world should know who was responsible for and carried out this,” Peskov said.
He dismissed suggestions that the Russian ship could have been involved in the attack. “Russian ships cross the Baltic, that’s normal, and there are hundreds of photographs of Russian ships” in the area, Peskov added.
The explosions in the twin Nord Stream pipelines occurred in the exclusive economic zones of Denmark and Sweden, but not in their territorial waters. Neither pipeline was in operation at the time as supplies in Nord Stream 1 had been halted earlier in September by Russia, and Nord Stream 2 was never started after Germany cancelled its approval process.
Western intelligence has been increasingly worried about Russia appearing to test the vulnerability of critical infrastructure in European countries. One of two fibre optic cables linking the Norwegian mainland with the Arctic archipelago of Svalbard was cut in January, with police blaming human activity. Russian fishing boats were observed repeatedly sailing over the cable in an unusual pattern but no one has been officially blamed for the sabotage yet.