MOSCOW: Russia needs permission for its vessels to conduct investigations into explosions that damaged Nord Stream pipelines in the Baltic Sea, Deputy Prime Minister Alexander Novak said on Friday.

He did not specify who should grant the permission but Nord Stream AG, the operator of the older Nord Stream 1 pipeline, said last week that the owner of a survey vessel it chartered did not have the greenlight from the Norwegian foreign ministry to depart and start assessing ruptures to the pipelines.

"The whole question is in the access for our vessels, which should have rights of passage (to the area of the incidents)," Novak told reporters, commenting on Moscow's efforts to investigate the damage to the pipelines.

Russia said on Thursday it had summoned diplomats from Germany, Denmark and Sweden to complain that representatives from Moscow and Gazprom had not been invited to join an investigation into the leaks in the gas pipelines that run from Russia to Europe.

Sweden has previously rejected calls from Russian authorities to be part of the investigation or to share any findings before it is complicated.

The Danish foreign ministry said on Thursday "the Russian wish to participate in the investigation of the Nord Stream leaks has been brought up through diplomatic channels in Moscow and Copenhagen".

The cause of the damage to the Nord Stream pipelines remains unclear, but European Union countries have said they suspect sabotage, while Russia has called the incidents an "act of international terrorism" and blamed the West.