Sweden says it will be difficult to determine who blew up Nord Stream pipelines

Pipelines connecting Russia and Germany in the Baltic Sea were attacked last year

The explosions caused two majority Russian-controlled pipelines to leak gas into the Baltic Sea. Reuters

Swedish prosecutors have said it is going to be "difficult" to find out who blew up the Nord Stream pipelines in the Baltic Sea last year.

Seven months into the investigation of the explosions that ruptured the pipelines connecting Russia and Germany in the economic zones of Sweden and Denmark at a depth of 80 meters, prosecutors said investigation was complicated.

"Our hope is to be able to confirm who has committed this crime, but it should be noted that it likely will be difficult given the circumstances," prosecutor Mats Ljungqvist said.

"We are working unconditionally and turning over every stone and leaving nothing to chance."

Mr Ljungqvist said that "the clear main scenario" was that a state sponsored group was behind the sabotage but that an independent group was still "theoretically possible".

He said that the type of explosive used in the bombings ruled out "a large portion of actors".

The landfall facilities of the Nord Stream 1 gas pipelines in Lubmin, Germany. Reuters

Germany has confirmed its investigators raided a ship in January that may have been used to transport the explosives used to blow up the pipelines. The boat could have been used by a Ukrainian or pro-Ukrainian group, German media reported.

"There is a variety of information and reports about the sabotage against the gas pipes. The incident has obviously become an open arena for different influence attempts," Mr Ljungqvist said.

"These speculations do not have an impact on the ongoing investigation, which is grounded in facts and the information which has emerged from analyses, crime scene investigations and collaboration with authorities in Sweden and other countries."

Last week the UN Security Council rejected Moscow's draft resolution calling for an independent inquiry into the sabotage.

The draft resolution stated the attack was carried out by a state actor and that a UN investigation is needed to “uncover the truth and identify those responsible".

It was co-sponsored by China, Belarus, Venezuela, North Korea, Nicaragua, Syria and Eritrea.

Moscow alleges that the three nations are engaged in a US-backed cover-up and has rejected its repeated requests for a joint investigation.