A fourth leak on the Nord Stream pipelines has been reported off southern Sweden, the country’s coast guard said on Thursday, after explosions were reported earlier this week in suspected sabotage.

Sweden’s coast guards told news agency TT that they have a vessel on the site of the leak, off Sweden. All four detected leaks are in international waters, two near Sweden and two near Denmark.

The European Union suspects sabotage was behind the gas leaks on the subsea Russian pipelines to Europe and has promised a "robust" response to any intentional disruption of its energy infrastructure.

"Two of these four are in Sweden’s exclusive economic zone," coast guard spokesperson Jenny Larsson told the Svenska Dagbladet newspaper late on Wednesday.

The Nord Stream pipelines run through the Baltic to transport gas from Russia to Germany. While neither pipeline was in use at the time of the suspected blasts, they were filled with gas that has been spewing out in the Baltic Sea since Monday’s ruptures.

The fourth leak was on the Nord Stream 2 pipeline, in close proximity to a larger hole found on the nearby Nord Stream 1, the Swedish coast guard said.

The Danish and Swedish governments believe that the leaks off their countries were "deliberate actions."

Before the leaks were reported, explosions were recorded. A first explosion was recorded by seismologists early Monday southeast of the Danish island of Bornholm. A second, stronger blast northeast of the island that night was equivalent to a magnitude 2.3 earthquake. Seismic stations in Denmark, Norway and Finland also registered the explosions.

Some European officials and energy experts have said Russia is likely to blame for any sabotage – it directly benefits from higher energy prices and economic anxiety across Europe – although others cautioned against pointing fingers until investigators are able to determine what happened.