LONDON (AA) - Sweden on Thursday said suspicions of gross sabotage in the recent Nord Stream gas leaks had strengthened after a preliminary investigation, according to local media.

"Detonations" caused "extensive damage" to both the Nord Stream 1 and 2 pipelines, public broadcaster SVT Nyheter reported, citing the Swedish Security Service (SAPO) intelligence agency.

Underlining that Swedish authorities would analyze the damage to the pipelines, SAPO chief Karl Melin stopped short of giving details on the damage as that would be "endangering" to the investigation, according to the outlet.

In a press release on the matter, the Swedish Public Prosecutor's Office highlighted the gravity of the situation, adding that the "authorities involved are fulfilling their respective tasks in the best possible way."

Sweden's outgoing Prime Minister Magdalena Andersson also said the gas leaks were likely not a coincidence.

"It is likely that a deliberate act -- in other words, sabotage -- caused the leaks, which are located in the Swedish and Danish economic zones. This is thus not a direct attack on Sweden," said Andersson in a statement published on the government's website.

Sweden's Foreign Minister Ann Linde, for her part, said the incident was the most serious security policy issue that Sweden has faced since 1980, SVT Nyheter reported.

She added that the situation of the Nord Stream 1 and Nord Stream 2 should be seen as an sign "of the deteriorating security policy" in and near Europe.

"At the moment, we are not sure who did it. However, the suspicion of sabotage should not be perceived as a military threat to Sweden," Linde said.

SAPO launched an investigation into the incident after four leaks were identified in the Russian-owned pipelines, which run from Russia to Germany and pass through both Denmark and Sweden's exclusive economic zones in the Baltic Sea.

The two Nordic countries raised suspicions soon after the leaks were detected that they were caused by two undersea explosions and were the result of a deliberate act.

Similar sentiments were echoed by the EU, which said the gas leaks were not accidental.

The Danish Energy Agency and Russian energy company Gazprom had announced earlier that the pressure levels in the pipelines have returned to normal, indicating that the gas leaks have stopped.

Leila Nezirevic/AA