Information gathered on the damage to the Nord Stream 1 and 2 pipelines in the Baltic Sea suggest "the result of deliberate, reckless, and irresponsible acts of sabotage," the North Atlantic Council said Thursday.
Damage to the pipelines is of "deep concern," the council said in a statement.
"These leaks are causing risks to shipping and substantial environmental damage. We support the investigations underway to determine the origin of the damage," the statement said.
"We, as Allies, have committed to prepare for, deter and defend against the coercive use of energy and other hybrid tactics by state and non-state actors. Any deliberate attack against Allies’ critical infrastructure would be met with a united and determined response," it added.
More context: Earlier Thursday, Germany's ambassador to the UK said there was a "very strong indication" the pipeline leaks were acts of sabotage. US National Security Adviser Jake Sullivan also labelled the leaks "apparent sabotage" in a tweet Tuesday.
European security officials observed Russian navy ships in the vicinity of leaks on Monday and Tuesday, according to Western intelligence officials and one other source. Senior Western officials have stopped short of attributing the attack to Russia or any nation.
What the Kremlin is saying: A Russian government spokesperson said Thursday that the leaks may have been the result of a "terrorist attack."
"The unprecedented nature of this event, it seems that this is a terrorist attack, possibly at the state level," Kremlin spokesperson Dmitry Peskov said during a daily call with journalists.
Asked about CNN's report on Russian submarines seen in the area of the Nord Stream disruptions, Peskov said: “This is the Baltic sea. There were far more aircraft, floating and other marine vehicles that belong to NATO countries seen there."
CNN's Anna Chernova, Allegra Goodwin and Radina Gigova contributed reporting to this post.