Russia said on Thursday that leaks spewing gas into the Baltic Sea from pipelines to Germany appeared to be the result of state-sponsored “terrorism”, as an EU official said the incident had fundamentally changed the nature of the conflict in Ukraine.

The European Union is investigating the cause of the leaks in the Gazprom-led (GAZP.MM) Nord Stream 1 and 2 pipelines and has said it suspects sabotage was behind the damage off the coasts of Denmark and Sweden.

Four days after the leaks were first spotted, it remains unclear who might be behind any attack on the pipelines that Russia and European partners spent billions of dollars building.

“This looks like an act of terrorism, possibly on a state level,” Kremlin spokesman Dmitry Peskov said, adding: “It is very difficult to imagine that such an act of a terrorism could have happened without the involvement of a state of some kind”.

Russia also said the United States stood to benefit, in a war of words with the West over who was responsible. Moscow has previously said the leaks occurred in territory that is “fully under the control” of U.S. intelligence agencies.

Russia’s Foreign Ministry spokeswoman Maria Zakharova told a news briefing Washington would be able to boost its liquefied natural gas (LNG) sales if the pipelines were put out of use.

But U.S. news channel CNN, citing three sources, reported that European security officials had observed Russian navy support ships and submarines not far from the leaks.