This file photo provided by the Swedish Coast Guard on Sept. 28, 2022 shows a gas leak on the Nord Stream 1 pipeline. (The Swedish Coast Guard/Handout via Xinhua)

"There is no doubt that this is gross sabotage in international waters directed towards infrastructure," said Ljungqvist, "The focus for the Swedish investigation is primarily about examining if Swedish interest or Swedish security is threatened, for example if Swedish territory was used to carry out the sabotage."

STOCKHOLM, April 6 -- Sweden's public prosecutor Mats Ljungqvist has said here on Thursday that due to the "complex" nature of the sabotage of the Nord Stream 1 and 2 pipelines, the investigation has yet to determine who is responsible.

"This concerns a crime whose circumstances are difficult to investigate. The detonations took place 80 meters under the water on the ocean floor in the Baltic Sea," said Ljungqvist, who is in charge of the ongoing investigation.

Picture taken on Oct. 8, 2012 shows Nord Stream pipeline equipments before the opening ceremony of the North Stream second gas link in Portovaya bay, some 60 kilometers from the town of Vyborg in northwestern Russia. (Xinhua) 

According to the Swedish Prosecution Authority, the investigation is being conducted by the Swedish Security Service under the management of the public prosecutor at the Swedish Prosecution Authority.

Previously, the investigation has been able to confirm that this is a case concerning gross sabotage. Analyses from objects seized during the crime scene investigations show traces of explosives on several of the foreign objects found at the site, says the Authority.

"There is no doubt that this is gross sabotage in international waters directed towards infrastructure," said Ljungqvist, "The focus for the Swedish investigation is primarily about examining if Swedish interest or Swedish security is threatened, for example if Swedish territory was used to carry out the sabotage."

Photo taken in Arlington of Virginia, the United States, shows a screen displaying U.S. President Joe Biden and German Chancellor Olaf Scholz (not pictured) attending a press conference at the White House in Washington, D.C. Feb. 7, 2022. Joe Biden told the press conference that if Russian tanks and troops cross the border and enter Ukraine, "there will be no longer Nord Stream 2," referring to the now-finished pipeline delivering natural gas from Russia to Germany through Ukraine. (Xinhua/Liu Jie)

The Nord Stream pipelines, which transported natural gas from Russia to European markets via Germany, were severely damaged last September by blasts in the Baltic Sea. Nord Stream 1 was in operation at the time of the explosion, while Nord Stream 2 was not operational at the time, but was filled with gas.

In February, Pulitzer Prize winner Seymour Hersh revealed that the United States partnered with Norway in a top-secret operation in June 2022 to plant remotely triggered explosives that took out three of the four Nord Stream pipelines three months later.