A Western official said the leaks in the gas pipeline were a very serious development, but a full investigation is needed to establish what happened.
“On the pipelines, clearly, this looks very serious. The multiple explosions at the same time - it’s very serious, and is going to have to be investigated,” the Western official said, on condition of anonymity.
“It definitely looks highly suspicious, but I think we need to establish the facts and then attribute.”
EU officials have meanwhile warned of retaliation in the form of a “robust and united response” for any further attack on Europe’s energy networks.
“All available information indicates those leaks are the result of a deliberate act,” Josep Borrell, the EU foreign policy chief, said on behalf on all 27 member states.
He continued: “Any deliberate disruption of European energy infrastructure is utterly unacceptable and will be met with a robust and united response.”
The caution is given at a time when the continent is battling crippling energy and cost of living crises that have already seen huge cutbacks in gas and electricity usage by both the state and individual households, as the EU countries attempt to build energy independence from Russia.
Explosions were discovered the Baltic Sea on Tuesday before unusual leaks were discovered on two underwater natural gas pipelines running 230 kilometres (764 miles) from Russia through the Baltic Sea to Germany.
The three leaks were reported on the Nord Stream 1 and 2 pipelines, which are filled with natural gas but are not delivering the fuel to Europe.
The damage means that the pipelines are unlikely to be able to carry any gas to Europe this winter even if the political will to bring them online emerged, according to analysts.
The first explosion was recorded early on Monday southeast of the Danish island of Bornholm.
A second, stronger blast northeast of the island that night was equivalent to a magnitude 2.3 earthquake. Seismic stations in Denmark, Norway, and Finland also registered the explosions.
Mr Borrell said the EU will support any investigation into the damage, and “will take further steps to increase our resilience in energy security”.
NATO Secretary-General Jens Stoltenberg also attributed the leaks on the Nord Stream pipelines to acts of sabotage and said he had discussed the protection of critical infrastructure in NATO countries with the Danish defence minister.
“Discussed the sabotage on the NorthStream pipelines with Defence Minister Morten Badskov,” he said on Twitter.
“We addressed the protection of critical infrastructure in NATO countries.”
Danish prime minister Mette Frederiksen has said that “it is the authorities’ clear assessment that these are deliberate actions - not accidents”.
But she said “there is no information indicating who could be behind it”.
Ms Frederiksen rejected the suggestion that the incident was an attack on Denmark, saying the leaks occurred in international waters.