Russian Foreign Minister Sergei Lavrov said on Wednesday it appeared no European countries were conducting a proper investigation into the series of explosions that ruptured the Nord Stream gas pipelines in September.
"After the explosions on Nord Stream - which, it appears nobody in the European Union is going to objectively investigate - Russia stopped gas transportation through the northern routes," Lavrov said.
Russia has blamed Britain for the explosions - claims rejected by London. Investigators in Sweden and Denmark say they were the deliberate results of sabotage, though they have not named any possible culprits.
The Washington Post, quoting diplomats and intelligence officials, reported on Wednesday that no conclusive evidence had emerged to suggest that Russia itself was behind the attacks, as some Western governments and analysts had claimed in the immediate aftermath.
It said some of the sources now believed it may be impossible to establish who was to blame.
The Nord Stream 1 and Nord Stream 2 pipelines have a joint annual capacity of 110 billion cubic metres - more than half of Russia's normal gas export volumes. Sections of the 1,224-km (760-mile) long pipelines, which run from Russia to Germany, lie at a depth of around 80-110 metres, and Moscow says no decision has yet been taken on whether to attempt to repair them.
(Reporting by ReutersEditing by Mark Potter)