Traces of explosives have been found at the Baltic Sea site where natural gas pipelines were damaged in an act of "gross sabotage", according to a Swedish prosecutor. 

Mats Ljungqvist of the Swedish Prosecution Authority said investigators carefully documented the area where the Nord Stream 1 and 2 pipelines ruptured in September, causing significant methane leaks.

The parallel undersea pipelines run from Russia to Germany.

"Analysis carried out shows traces of explosives on several of the foreign objects that were found," Mr Ljungqvist said in a statement.

The prosecution authority said the preliminary investigation was "very complex and comprehensive" and further scrutiny would show whether anyone could be charged "with suspicion of crime".

Investigators in Sweden, Denmark and Germany are looking at what happened.

Danish officials confirmed in October "powerful explosions" had caused extensive damage to the pipelines.

The leaks, which stopped after several days, happened in international waters but within the exclusive economic zones of Denmark and Sweden.

Investigators have not yet said who they think may be responsible but reported earlier the blasts were likely to have involved several hundred pounds of explosives.

Kremlin spokesman Dmitry Peskov said on Friday it was "very important to find those who are behind the explosion".

Sweden's findings of "a sabotage act or a terrorist act -- you can call it whatever you like" confirm "the information that the Russian side has had," he said.

Moscow needs to wait for a full damage assessment to decide whether to repair the pipelines, he said.

Nord Stream 1 carried Russian gas to Germany until Moscow cut off supplies at the end of August.

Nord Stream 2 never entered service as Germany suspended its certification process shortly before Russia invaded Ukraine in February.

'No information on who is behind sabotage'

The governments of Denmark, Germany and Sweden have withheld speculation over who may be behind the leaks, saying only there's not enough proof yet to identify them. 

"We have no information on possible initiators of this act of sabotage," German Chancellor Olaf Scholz's spokesman, Steffen Hebestreit, said at a regular government news conference in Berlin on Friday.

But some Nordic and other European media outlets have pointed a finger of blame on Moscow, hosting military experts suggesting  Russia has all the resources to carry out such a precise attack requiring careful advance planning.

Fatih Birol, head of the International Energy Agency, said in late September it was "very obvious" who was responsible of the pipeline sabotage, suggesting Russia's involvement.

Russian President Vladimir Putin has accused the West of blowing up the pipelines and singled out the United States as profiting from attacks on Europe's energy infrastructure.

Earlier this week, Germany completed port facilities for the first of five planned liquefied natural gas terminals it is scrambling to get running as it replaces the Russian pipeline gas which once accounted for more than half its supplies.

AP