The Swedish Coast Guard says it has discovered a fourth gas leak on the damaged Nord Stream pipelines in the Baltic Sea.

The hole was also found this week, the newspaper "Svenska Dagbladet" quoted a spokesman for the coast guard on Thursday.

The Coast Guard said two of the leaks would be in Denmark's economic zone and two in Sweden's.

On the night of Monday, a sharp drop in pressure was initially detected in one of the two tubes of the unused Nord Stream 2 pipeline.

Later, the Nord Stream 1 operator reported a drop in pressure in these two tubes as well.

Danish authorities eventually discovered a total of three leaks in the two pipelines near the Danish island of Bornholm.

Kremlin rejects speculation about Russian involvement

Already on Tuesday, several countries brought an attack on the European gas infrastructure into play as the cause of the unprecedented damage.

The EU and NATO assume sabotage.

On Wednesday, the Kremlin dismissed speculation that Russia was involved in the damage to the pipelines as "stupid and absurd".

According to the Danish Energy Agency, more than half of the gas has already escaped from the affected lines.

The lines should therefore probably be empty on Sunday, as the head of the authorities, Kristoffer Böttzauw, said at a press conference on Wednesday.

According to calculations by the authority, the climate impact of the gas leak corresponds to around one third of Denmark's total climate impact in one year.

A concrete health risk for the population - especially on the Baltic Sea island of Bornholm - does not exist, it said.

EU Interior Commissioner Ylva Johansson described the alleged sabotage of the pipelines as a warning call and announced a stress test for critical infrastructure in Europe.

"We will now contact all member states and we will carry out a stress test in relation to the critical infrastructure," said the Swede on Wednesday evening on ZDF's "heute journal".

In view of the leaks in the pipelines, she spoke of an "attack" that was an "escalation" and "a threat".

"As far as I can tell, it is a very intelligent attack that cannot have been carried out by a normal group of people," said the Commissioner.

The risk is great that a state is behind it.

"Of course we have our suspicions.

But it's too early to make a final judgement."

Price: Currently have more questions than answers

US State Department spokesman Ned Price was similarly cautious about possible causes of the pipeline leaks.

"We currently have more questions than answers." The US government does not want to make any assumptions about possible backers of a sabotage action until investigations into the natural gas pipelines have been completed.

The Russian Prosecutor General's Office has meanwhile opened a case of international terrorism.

Moscow justified the step by saying that the damage to the pipelines had "inflicted considerable economic damage on Russia".

Gazprom pumped gas to Europe through Nord Stream 1 until the end of August, but then stopped these deliveries, citing technical problems that allegedly could not be solved due to sanctions.

The federal government called the reason advanced and suspected political motives behind the delivery stop.

Nord Stream 2 was also filled with Russian gas.

Moscow has repeatedly offered the pipeline as a possible replacement for Nord Stream 1 in recent months, but Germany has not certified the pipeline.

Since the start of the Russian war of aggression against Ukraine, commissioning has been ruled out.

The Internet newspaper lenta.ru, which is considered to be close to the Kremlin, reported that a US helicopter circled the Baltic Sea for nine hours from Sunday evening to Monday morning, about 250 kilometers from the Danish island of Bornholm.

The newspaper relied on data from Flightradar.

The MH-60R Strike Hawk multi-purpose helicopter can also fight underwater targets, the Internet newspaper emphasized.

US Secretary of Defense Lloyd Austin spoke to his Danish colleague Morten Bødskov about the pipeline incidents.

Lloyd Denmark offered the "full support" of the US government with a view to the beginning investigations into the "explosions", as the ministry announced on Wednesday (local time).

"The United States remains committed to security in the Baltic Sea and to our longtime ally Denmark," it said.

The ministers agreed to work together as the matter progressed, the US Department said.

A UN spokesman, meanwhile, expressed concern about the possible environmental impact of the pipeline leaks.

One hopes that the responsible authorities will seal the leaks as soon as possible.

Ex-BND President Gerhard Schindler suspects Russia is behind the pipeline leaks because he believes it has the most to gain from the damage.

"The stop in gas deliveries can now be justified simply by referring to the defective lines, without having to advance alleged turbine problems or other unconvincing arguments for breaking the supply contracts," Schindler told Welt.

"Unnoticed, conspiratorial damage to pipelines at a depth of 80 meters in the Baltic Sea" also clearly points to a state actor.

Schindler was head of the BND from late 2011 to mid-2016.