NATO has condemned the suspected sabotage of the Nord Stream pipelines as “deliberate, reckless and irresponsible” but stopped short of blaming Russia.
The treaty organisation warned the explosions could case risks to shipping alongside severe environmental damage.
It supported investigations into the leak and said it would defend member states from attacks on infrastructure, without naming a culprit.
NATO 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.”
The European Union has also promised a “robust” response to any intentional attacks on its energy infrastructure, but it also refused to link anyone to the sabotage.
“Any deliberate disruption of European energy infrastructure is utterly unacceptable and will be met with a robust and united response,” the EU foreign policy chief Josep Borrell said.
However, Ukraine has blamed Russia for a “terrorist” act on the pipelines, amid speculation the Kremlin was looking to fire a warning shot to the West – which has impsed
The Kremlin has denied any involvement in the explosions, with Russia’s foreign ministry arguing that the blasts had occurred in territory “fully under the control” of US intelligence agencies.
“It happened in the trade and economic zones of Denmark and Sweden,” spokeswoman Maria Zakharova told a pro-Kremlin broadcast.
A British defence source told Sky News they were likely premeditated attacks using underwater explosives.
It said the mines could have been lowered on a long line, dropped over a boat or placed next to the pipelines with an underwater drone.
Nord Stream gas could stop leaking on Monday
This follows explosions reported across the multi-billion Nord Stream 1 and 2 pipelines earlier this week, with four leaks identified along the Baltic Sea pipelines.
The fourth leak was announced today by Swedish authorities observing the pipeline route.
Neither pipeline was in operation, with Nord Stream 1 halted amid a dispute over sanctions and maintenance, while Nord Stream 2 was never approved for operations.
However, the pipes were still filled with natural gas and scientists predict as much as 350,000 tonnes of methane could have been released into the sea following the explosions.
This would make the event one of the worst natural gas leaks in recorded history.
So far, it has caused patches of gas bubbles to stretch over 1km across the surface of the Baltic Sea.
The pipelines do not have mechanisms to halt the flows across the pipeline, meaning it is expected gas flows from the entire pipeline will eventually leak into water.
Gas prices rallied earlier this week following the news amid fears of future unpredictability, but have since eased with the UK and Dutch benchmarks down 19 and 11 per cent today.
The pipeline’s operator Nord Stream AG predicts gas will likely stop leaking from the damaged Nord Stream pipelines on Monday.
A Nord Stream AG spokesperson told news agency Reuters it was not possible to provide any forecasts for its future operations until the damage had been assessed.
It said: “Until there are some results from an assessment of the damage, no forecasts can be made. The damage assessment can be carried out on the spot as soon as we manage to approach the area. At the moment it is a restricted zone.”