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Officials said the gas would be directed elsewhere and blamed Russia for the situation.
The operator of Ukraine’s gas system, GTSOU, said it would stop shipments via the Sokhranivka route from Wednesday, declaring “force majeure”, a clause invoked when a business is affected by something beyond its control.
The company said it could not operate at the Novopskov gas compressor station due to “the interference of the occupying forces in technical processes”.
To fulfil its “transit obligations to European partners in full”, it said it could "temporarily transfer unavailable capacity" to the Sudzha physical interconnection point located farther to the west in territory controlled by Ukraine.
But Gazprom, which holds a monopoly on Russian pipeline gas exports, said it was “technologically impossible” to shift all volumes to the Sudzha interconnection point.
GTSOU chief executive Sergiy Makogon told Reuters that Russian forces had begun commandeering gas transiting through Ukraine and sending it to two Russia-backed separatist regions in the country's east, though he did not cite evidence to support his claims.
Ukraine's suspension of Russian natural gas flows through the Sokhranivka route should not have an impact on the domestic Ukrainian market, state energy firm Naftogaz head Yuriy Vitrenko told Reuters.
The state gas company in Moldova, a small nation on Ukraine's western border, said it had not received any notice from GTSOU or Gazprom that supplies would be interrupted.
The Novopskov compressor station in the Luhansk region of eastern Ukraine was occupied by Russian forces and separatist fighters soon after Moscow began what it describes as a “special military operation” on February 24.
It is the first compressor in the Ukrainian gas transit system in the Luhansk region and the transit route for about 32.6 million cubic metres of gas a day — a third of the Russian gas that is piped to Europe through Ukraine, GTSOU said.
Gazprom said it had received notification from Ukraine that the country would stop the transit of gas to Europe via the Sokhranivka interconnector from 0700 local time on Wednesday.
The Russian company said it had seen no proof of force majeure or obstacles to continuing as before. Gazprom added that it was meeting all obligations to buyers of gas in Europe.
The US has urged countries to decrease their dependence on Russian energy and has banned oil and other energy imports from Russia in retaliation for its invasion of Ukraine.
US State Department spokesman Ned Price said that Tuesday's announcement does not change the drive to decrease global dependence on Russian oil “as soon as possible”.