NATO said Thursday it would retaliate for any attacks on the critical infrastructure of its 30 member countries as it suggested that damage to two gas pipelines off Denmark and would-be member Sweden in international waters in the Baltic Sea is the result of sabotage.

Any deliberate attack against Allies critical infrastructure would be met with a united and determined response, NATO ambassadors said in a statement. They said that the damage to the pipelines between Russia and Germany is of deep concern.

The alliance also said that all currently available information indicates that this is the result of deliberate, reckless, and irresponsible acts of sabotage. These leaks are causing risks to shipping and substantial environmental damage.

Danish Defence Minister Morten Bodskov on Twitter called it a joint condemnation and very strong signal from the alliance.

The Swedish coast guard on Thursday confirmed a fourth leak on the Nord Stream pipelines off southern Sweden.

We have leakage at two positions off Sweden, coast guard spokesperson Mattias Lindholm. There are two more off Denmark, he said.

Two of the leaks are on the Nord Stream 1 pipeline that recently stopped supplying gas, while the other two are on Nord Stream 2 that never started operating. Although they werent running, both pipelines were filled with gas, which has escaped and bubbled to the surface.

The Nord Stream pipelines run through the Baltic to transport gas from Russia to Germany. 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.

Speaking Wednesday before the fourth leak was reported, Swedish Prime Minister Magdalena Andersson said it would have taken a large explosive device to cause the damage.

In Moscow, Kremlin spokesman Dmitry Peskov said Thursday that the Nord Stream pipeline incident would have been impossible without a state actors involvement.

It looks like a terror attack, probably conducted on a state level, Peskov said in a conference call with reporters.

Judging by the amount of destruction of the Nord Stream, its hard to imagine that such action could have been taken without a state involvement, Peskov said. Its a very dangerous situation that requires a quick investigation.

He dismissed media reports about Russian warships spotted in the area as stupid and biased, adding that many more aircraft and vessels belonging to NATO countries have been spotted in the area.

Torben Mikkelsen, a former admiral with the Danish navy, told The Associated Press that it was not so demanding to carry out an operation either by using a remotely operated underwater vehicle or sending divers from a submarine or a surface vessel.

Those who carried out the operation knew they wouldnt get caught, Mikkelsen said. Who would have thought of an operation against pipelines in the Baltic Sea?