Russia’s main gas pipeline to Europe will not reopen as planned on Saturday, adding to concerns about energy supplies this winter.
State energy firm Gazprom said it found a leak on Nord Stream 1, meaning it could be closed indefinitely.
The pipeline, which runs to Germany, has been shut for three days for what Gazprom described as maintenance work.
Europe accused Russia of using its gas supplies to blackmail Europe amid the Ukraine conflict, which Moscow denies.
Energy prices have soared since Russia invaded Ukraine and scarce supplies could push up costs even further.
There are growing fears families in the EU will be unable to afford the cost of heating this winter.
As a result, international gas prices have fallen in the past week, but remain high by normal standards.
Europe is attempting to wean itself off Russian energy in an effort to reduce Moscow’s ability to finance the war, but the transition may not come quickly enough.