Russia's Baltic Fleet has bases in Baltiysk (Kaliningrad Oblast) and Kronstadt. Fleet assets range from at least one SSK to multiple surface warships to various specialized auxiliaries. Russian ships would be cruising the Baltic with some frequency.
I don't see any clear reason the US would sabotage/attack the pipelines. Russia has cut off the flow of gas, and domestic energy supply would not be diminished. I have a hard time imagining PINO Biden doing anything so decisive.
OTOH, while Russia is obviously using its natural gas to armtwist EuroLand, I see no reason Russia would destroy that leverage. I guess a false claim that the US did it could be used to create a siege mentality in Russia, but

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Similarly, I don't see why any Baltic country - Poland, the Baltic states, Finland or a Scandinavian country - would sabotage/attack the pipelines. They all rightly fear Russia, but the pipelines lack military value, and this would be likely to antagonize Russia and lead to retaliatory attacks.
I seriously wonder if it was done by non-state actors, specifically Enviros, wanting to cut off EuroLand from the evil fossil fuel, natural gas. I'm persuadable, as evidence surfaces.