The European Union says leaks in two major gas pipelines from Russia to Europe were caused by sabotage, but stopped short of directly accusing Russia.
European Commission President, Ursula von der Leyen, says deliberate disruption would meet the “strongest possible response”.
The EU has previously accused Russia of using gas supplies as a weapon against the West over its support for Ukraine.
However, the Kremlin has dismissed the accusations, calling them “predictable, stupid and absurd”.
Authorities say leaks were likely to last for at least a week, until the gas escaping from the pipes runs out.
The Nord Stream 1 pipeline – which consists of two parallel branches – has not transported any gas since August when Russia closed it down, saying it needed maintenance.
It stretches 745 miles under the Baltic Sea from the Russian coast near St Petersburg to north-eastern Germany.
Its twin pipeline, Nord Stream 2, was halted after Russia invaded Ukraine in February.
