Russia said on Thursday that leaks spewing gas into the 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 Nord Stream 1 and 2 pipelines under the Baltic Sea and has said it suspects sabotage.
It remains unclear who might be behind any deliberate 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 told reporters.
"It is very difficult to imagine that such an act of terrorism could have [happened] without the involvement of a state of some kind," Peskov said. "This is a very dangerous situation which requires an urgent investigation."
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 sites of the leaks.
Asked to comment on the CNN report, Peskov said there had been a much larger NATO presence in the area.
Russia has also said the leaks off the coasts of Denmark and Sweden occurred in territory that is "fully under the control" of U.S. intelligence agencies.
EU leaders will discuss next week at a summit in Prague what the bloc has denounced as sabotage of the gas pipelines, an EU official said, as gas continued to spew into the Baltic Sea for a fourth day since leaks were first detected.
The gas leak at Nord Stream 2 seen from the Danish F-16 interceptor on Bornholm. Photo: Danish Defence
"The attack on strategic infrastructure means that the strategic infrastructure in the entire EU has to be protected," the EU official in Brussels said.
"This changes fundamentally the nature of the conflict as we have seen it so far, just like the mobilisation ... and the possible annexation," the EU official said, referring to Russia's mobilizing of more troops for the war and expectations President Vladimir Putin will annex Ukrainian regions.
Russia's war with Ukraine and the resulting energy standoff between Moscow and Europe, which has left the EU scrambling to find alternative gas supplies, are set to dominate the EU summit on Oct. 7 in Prague.
The European Union on Wednesday warned of a "robust and united response" should there be more attacks and stressed the need to protect its energy infrastructure, but EU officials have avoided pointing a figure directly at possible perpetrators.
The Nord Stream 1 and 2 pipelines were not supplying gas to Europe when the leaks were first detected on Monday but still had gas in them. Russia had halted deliveries via Nord Stream 1, saying Western sanctions had hampered operations. Nord Stream 2 had not started commercial operations.
Next week, EU leaders will discuss an eighth sanctions package on Russia which European Commission chief Ursula von der Leyen has proposed, including tighter trade restrictions, more blacklistings and an oil price cap for third countries.
The EU official said he expected the 27-nation bloc to agree parts of the sanctions package before the Prague summit, such as the blacklisting of additional individuals and some of the trade restrictions with regard to steel and technology.
Other topics such as the oil price cap or the sanctioning of banks may not be solved before the summit, he added.
EU states need unanimity to impose sanctions and Hungary's prime minister Viktor Orban has been a vocal critic, saying sanctions have "backfired", driving up energy prices and dealing a blow to European economies.
"Hungary has done a lot already to maintain European unity but if there are energy sanctions in the package, then we cannot and will not support it," Orban's chief of staff Gergely Gulyas told a briefing on Thursday.
(Reuters - Writing by Alexander Smith; Editing by Elaine Hardcastle)