On Wednesday, Western allies cautioned against drawing hasty judgments about who was responsible for the explosion of the Nord Stream pipelines. Germany even suggested that the incident may have been a “false flag” operation to put the blame on Ukraine.

Following Russia’s invasion of Ukraine last year, the New York Times reported on Tuesday that a pro-Ukrainian group may be responsible for the explosions that caused a diplomatic crisis between the West and Russia.

The report, while not pointing to any official Ukrainian involvement, comes at a time when Kyiv is urging its Western allies to ramp up supplies of high-end weapons to drive back Russian forces as the war enters its second year.

“There are ongoing national investigations and I think it’s right to wait until those are finalized before we say anything more about who was behind it,” said NATO Secretary-General Jens Stoltenberg.

Investigations continue into what caused the Nord Stream pipelines, supplying Russian energy to Europe, to rupture and spew bubbles of natural gas into the Baltic Sea last September. Western countries believe the explosions were deliberate but have not concluded who was behind them.

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.

A separate report by Germany’s ARD broadcaster and Zeit newspaper said on Tuesday 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.

“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 Defense Minister Boris Pistorius said on Wednesday.

“But I am warning against jumping to conclusions,” Pistorius said on the sidelines of a summit in Stockholm.

Pistorius said earlier the likelihood was “equally high” that it could have been a “false flag operation staged to blame Ukraine”.

Germany, meanwhile, confirmed its investigators had raided a ship in January that may have been used to transport the explosives used to blow up the pipelines.

But a statement by the federal prosecutor said there was no reliable information yet on motives or perpetrators, including on whether the attack was state-sponsored.

“There is no suspicion against employees of the German company that rented out the ship,” it added.

European Union foreign policy chief Josep Borrell told reporters: “As long as investigations into Nord Stream blasts are ongoing, we can not draw conclusions.”