Leaked US intelligence suggests a pro-Ukrainian group may be behind the September 2022 attacks on the gas pipelines.

While not pointing to any official Ukrainian involvement, a New York Times report published on Tuesday said intelligence reviewed by United States officials found a pro-Kyiv group may be behind the attacks in September, which became a flashpoint between the West and Russia after last year’s Russian invasion of Ukraine.

“There are ongoing national investigations and I think it’s right to wait until those are finalised before we say anything more about who was behind it,” Stoltenberg said on Wednesday.

The explosions on the pipelines connecting Russia and Germany took place on September 26 in the exclusive economic zones of Sweden and Denmark. Both countries have concluded the blasts were deliberate but have not said who might be responsible.

Russia, which has previously blamed the West, seized on the news on Wednesday to demand a transparent investigation in which it also wants to participate.

Kremlin spokesman Dmitry Peskov suggested the media reports were a coordinated bid to divert attention and questioned how US officials could assume anything about the attacks without an investigation.

Ukrainian Defence Minister Oleksii Reznikov said the media reports were a “little bit strange” and had “nothing to do” with the Ukrainian government.

Reznikov said he was not worried about the prospect of the media reports weakening support for Ukraine.

Germany warned against “jumping to conclusions”.

“We have to make a clear distinction whether it was a Ukrainian group, whether it may have happened at Ukrainian orders, or a pro-Ukrainian group [acting] without knowledge of the government,” German Defence Minister Boris Pistorius said on Wednesday.

Pistorius said on the sidelines of a summit in Stockholm that the likelihood was “equally high” that it could have been a “false flag operation staged to blame Ukraine”.

Meanwhile, Germany’s federal prosecutor confirmed that investigators had raided a ship in January that may have been used to transport the explosives used to blow up the pipelines, but said there was no reliable information yet on motives, perpetrators, or whether the attack was state-sponsored.

European Union foreign policy chief Josep Borrell told reporters that there was “no suspicion against employees of the German company that rented out the ship”.

“As long as investigations into Nord Stream blasts are ongoing, we can not draw conclusions,” Borrell said.

Germany’s ARD broadcaster and Zeit newspaper said on Tuesday that the operation to place explosives on the seabed was carried out by six people, five men and one woman, who used forged passports.

They transported explosives on a yacht rented from a German charter company by a Poland-based firm owned by Ukrainian citizens, according to the report and prosecutors.