The European Union has warned that any deliberate attack on European energy infrastructure would be met with the “strongest possible response,” calling what it suspects is an intentional attack “utterly unacceptable.”

Most Western governments have stopped short of pointing the finger directly at Russia, while the Kremlin has sought to pin the blame on the West.

U.S. President Joe Biden described the blasts on the Nord Stream pipelines as a “deliberate act of sabotage” late last month, saying Washington was working with its allies to work out exactly what happened.

Fatih Birol, the executive director of the International Energy Agency, said at a conference in Paris last month that it was “very obvious” who was responsible for the gas leaks, Reuters reported. He did not say who that was, however.

Russia has denied it was responsible for the gas leaks. Russian Foreign Ministry spokesperson Maria Zakharova said at a briefing on Thursday that such claims were “absurd,” according to Tass news agency.

Zakharova emphasized the “enormous investment” that the Kremlin took in the infrastructure project and lashed out at the West for blocking Moscow from taking part in the investigations.

The unexplained Nord Stream gas leaks pose serious questions about the incident’s environmental impact.

Climate scientists acknowledged in the aftermath of the event that it was hard to accurately quantify the exact size of the emissions and said the leaks are a “wee bubble in the ocean” compared with the massive amounts of methane emitted around the world every day.

Methane is 84 times more potent than carbon and doesn’t last as long in the atmosphere before it breaks down. That makes it a critical target for combatting climate change quickly while simultaneously minimizing other greenhouse gas emissions.