The Kremlin said on Thursday it doubted the attacks on the Nord Stream pipelines last September could have been carried out without state support.
Kremlin spokesman Dmitry Peskov's comments came after the New York Times this week reported that U.S. officials were looking into whether a pro-Ukrainian non-government group was responsible for the blasts.
"As for the pro-Ukrainian angle, you know, the idea that some Dr. Evil organized it, that's hard to believe. It was too difficult a task, which probably only a well-trained special state service was capable of - and there are not too many of them in our world," Peskov said when asked about the report.
The New York Times reported on Tuesday that new intelligence reviewed by U.S. officials suggests that a pro-Ukraine group - likely comprised of Ukrainians or Russians - attacked the Nord Stream gas pipelines, but that there are no firm conclusions.
Russia has repeatedly asked to be allowed to join the investigations into the blasts, which ruptured three of the four pipelines of the Nord Stream 1 and 2 gas links that connect Russia to Germany under the Baltic Sea.
Investigators in Sweden, Denmark and Germany are currently conducting separate probes.
"We continue to demand a quick and transparent investigation, we continue to demand that we be allowed to take part in this investigation," Peskov told reporters at a regular Kremlin briefing.
"It is necessary to identify who executed it and who ordered it. Committing a terrorist attack against a piece of critical international energy infrastructure is too dangerous a precedent," he added.
Peskov again denied the "absurd hypothesis" that Russia itself might have been behind the attacks on its own infrastructure.
(Reporting by Reuters; Writing by Jake Cordell; Editing by Gareth Jones)
