Two natural gas pipelines running from Russia to Germany developed multiple leaks in the past two days, leading to allegations from several European countries of sabotage by Moscow, Reuters reported.

On Tuesday, Sweden’s Maritime Authority issued a warning about two leaks in the Nord Stream 1 pipeline under the Baltic Sea. A day earlier, a leak was discovered on the nearby Nord Stream 2 pipeline.

The leaks were discovered to the North East and South East of the Danish island of Bornholm.

The Swedish Seismic Institute said that multiple underwater blasts were recorded prior to the leaks, AFP reported.

Visuals released by Denmark’s armed forces showed bubbles rushing to the surface of the sea. The armed forces said that the leaks had caused surface disturbance of over 1 kilometre in diameter.

Ukrainian presidential advisor Mythailo Podolyak alleged that the gas leak was a “terrorist attack” planned by Russia and an act of aggression towards the European Union. “[Russia] wants to destabilize economic situation in Europe and cause pre-winter panic,” he said.

Podolyak said that in view of the situation, Ukraine needed tanks, particularly German ones, as a security investment. Since February, Ukraine and Russia have been engaged in a military conflict, with Western countries largely backing the former country.

Poland’s Prime Minister Mateusz Morawiecki alleged that the leaks were caused by sabotage, The Guardian reported.

“Today we faced an act of sabotage, we don’t know all the details of what happened, but we see clearly that it’s an act of sabotage, related to the next step of escalation of the situation,” he said.

Kremlin spokesperson Dmitry Peskov, responding to a question on whether the leaks may have been caused by sabotage, said that “no version could be excluded”, according to the Associated Press.

The Nord Stream pipelines have been a significant point of tensions between Russia and Western countries since the conflict in Ukraine began. The United States has opposed the Nord Stream 2 project as it would increase Europe’s reliance on Russia for gas supplies.