Norway’s government said on Thursday it would restrict access to its ports by Russian fishing vessels, the latest tightening of security measures in the Scandinavian country following the discovery last week of major leaks in the Nord Stream gas pipeline, Reuters reported.

Russian trawlers will now only be allowed to visit three ports and must undergo security checks when they do, Foreign Minister Annikan Heitfeldt told a news conference.

Authorities in Sweden and Denmark were investigating four leaks from Russian gas pipelines discovered last week in the economic zones of Sweden and Denmark.

“Explosions occurred near Nord Stream 1 and 2 in the Swedish economic zone, which resulted in significant damage to the gas pipelines,” the Swedish police said in a statement.

Evidence has been taken from the scene and will be analyzed, and the area is no longer cordoned off while the investigation continues and will determine “whether anyone can be suspected and subsequently prosecuted,” Swedish authorities also said.

A Kremlin spokesman said Thursday that the investigation could not be objective without Russia’s participation, given that Russia had not been invited to participate.