Sweden is blocking off the area around the Nord Stream pipeline gas leaks in the Baltic Sea to enable an advanced diving vessel to investigate the cause of the suspected sabotage to the energy infrastructure.

The Swedish Prosecution Authority said on Monday that to further probe the "aggravated sabotage", the prosecutor in charge has decided "to block off the area in order to do a crime scene investigation".

Public prosecutor Mats Ljungqvist was quoted in the statement as saying that he understands 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," he said.

In a separate statement, the Swedish Coast Guard said that it had started enforcing the prosecutor's decision to block off an area with a radius of 5 nautical miles (9.26 kilometers) on Monday.

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

The Nord Stream pipelines were built to send natural gas from Russia to Germany as a vital source of energy for states in the European Union, especially its largest economy Germany. The newer of the two pipelines, Nord Stream 2, had never entered service. The approvals process was halted in the days before the outbreak of the Russia-Ukraine conflict in late February. The impact of that move, together with the later halt to supplies via Nord Stream 1 due to maintenance, caused deep concerns in the EU on energy security over the coming years, particularly for this winter. The leaks in the pipelines, first reported last week, exacerbated those concerns.

The four leaks detected are near the Danish island of Bornholm, with two each in Denmark's and Sweden's exclusive economic zones.

Sweden, Denmark and Germany have launched a joint investigation into the gas leaks.

The Swedish Coast Guard said that it could no longer spot gas emanating from the leak on the Nord Stream 1 pipeline, but bubbles from a small leak, about 30 meters in radius, could still be seen above the Nord Stream 2 pipeline on Monday afternoon.

Under investigation

Sweden sent a vessel capable of "advanced diving missions" on Monday to the leak sites to investigate the cause amid speculation that Russia or the United States could be behind the incident. Both Moscow and Washington have denied any involvement.

The EU and several of its member states have called the leaks sabotage but have stopped short of pointing the finger at any specific country.

Russian energy giant Gazprom said on Monday that gas had stopped leaking from the ruptured pipelines and flows could resume at the last remaining intact pipeline in the Nord Stream 2 network. But the suggestion is unlikely to be accepted by the EU, which is weighing up more sanctions on Russia.

Gas prices in Europe are now over five times higher than a year ago. The EU and its member states have been urging businesses and households to save energy or face the possibility of rationing in the winter.

Keisuke Sadamori, director of energy markets and security at the Paris-based International Energy Agency, said on Monday that the Russia-Ukraine conflict and sharp reductions in natural gas supplies to Europe are "causing significant harm to consumers, businesses and entire economies, not just in Europe but also in emerging and developing economies".

EU energy ministers adopted measures last Friday to curb high energy costs, including windfall profit taxes on energy firms. But they failed to agree on a gas price cap, which is opposed by countries including Germany.

On Tuesday, the upper house of Russia's parliament voted to approve the incorporation of four regions into Russia: Kherson, Donetsk, Lugansk and Zaporizhzhia.

In a session on Tuesday, the Federation Council unanimously ratified legislation to incorporate the four regions, following a similar vote in the State Duma, Russia's lower house, on Monday. The documents now go to the Kremlin for Russian President Vladimir Putin's final signature.

Agencies contributed to the story.