Swedish prosecutors said Monday that they had decided to block off the area around the Nord Stream pipeline leaks in the Baltic Sea while the suspected sabotage is being investigated.

To further the investigation into "aggravated sabotage," the prosecutor in charge had decided "to block off the area in order to do a crime scene investigation," the Swedish Prosecution Authority said in a statement. 

"The investigation continues; we are at an intensive stage," public prosecutor Mats Ljungqvist said.

"I understand the considerable public interest, but we are in the early stages of a preliminary investigation, and I can therefore not comment on details about which investigatory measures we are taking."

Sweden's coastguard announced that it had started enforcing the prosecutor's decision to ban access within five nautical miles (9.26 kilometers) of the pipeline on Monday.

"The prohibition means a ban on driving ships, anchoring, diving, fishing, driving underwater vehicles or carrying out geophysical mapping," the coastguard said.

Discovered on September 26, all four of the leaks are in the Baltic Sea off the Danish island of Bornholm.

Two of the leaks are in the Swedish exclusive economic zone, and the other two are in the Danish zone.

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The Swedish coastguard also said it could no longer observe gas from the leak on the Nord Stream 1 pipeline, but bubbles from a smaller leak could still be seen above Nord Stream 2 on Monday afternoon.

The pipelines were built to transport gas from Russia to Germany. The Swedish government has said that the explosions were most likely set off deliberately but has so far refrained from speculating who may be behind them.

The governments of Sweden and Denmark said the explosions were probably caused by hundreds of kilos of explosives in a joint letter to the United Nations Security Council, Danish TV2 reported on Friday.

"We take this situation very seriously, and the detonations must be viewed in the light of the security policy situation," Sweden's Prime Minister Magdalena Andersson said at a press conference on September 28.

In a press release issued the same day, the Swedish Security Service said it had opened a criminal investigation into "gross sabotage."

(With input from agencies)