To be fair, he did not directly say that the USA would sabotage the pipelines. But the ambiguity, without saying something along the lines of applying diplomatic pressure on the German government...
So, who has the means and motive to carry such an act.
Lest say Russia, they might be able to do it. However unless they planned it as a false flag, what would they gain that can not gain without simply stopping the flow of gas from their side. While letting open the possibility to restart supplying gas to use as leverage. So I consider it unlikely that Russia carried this out, I will put the odds at 30-40%. Since it can not be ruled out that they might have carried out a false flag. But I have not heard any signals about them claiming that they detected suspicious NATO submarine movements in the Baltic sea. And it would be embarrassing to claim the Ukrainian navy carried out the attack.
The USA/NATO, basically the same thing since it is effectively under US control anyway. We have Biden's ambiguous statement. They certainly have the capacity to do so. And the US foreign policy establishment would probably like the idea of a Europe more depended on America for their energy. But once again has to carried out in a way that might implicate other actors. Or else it might turn many in Europe hard against the US. Even more so with coming of winter here. And the already rising gas-prices. I will the odds at the moment at 35-40%. The motive and capacity is there. But it needs to be well executed out covert operation, with also keeping their European allies in the dark.
But the problem is considering the present circumstances. It might be better to be very skeptical about any claims made by both sides.