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 was investigated.

In order 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... 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," public prosecutor Mats Ljungqvist was quoted saying in the statement.

Sweden's coastguard announced in a separate statement that it had started enforcing the prosecutor's decision to block off an area of five nautical miles (9.26 kilometres, 5.75 miles) on Monday.

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

All of the four leaks, which were discovered on Monday last week, are in the Baltic Sea off the Danish island of Bornholm.

Two of the leaks are located in the Swedish exclusive economic zone, and the two others in the Danish one.

The Swedish coastguard also said it could no longer observe gas emanating 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 Nord Stream 1 and 2 pipelines, which connect Russia to Germany, have been at the centre of geopolitical tensions as Russia cut gas supplies to Europe in suspected retaliation against Western sanctions following Moscow's invasion of Ukraine.

While the pipelines are not currently in operation, they both still contained gas before they fell victim to apparent sabotage.

Both Washington and Moscow have denied responsibility for the leaks.