The latest disruption comes as the Ukrainian government has been reporting major progress in deliveries of gas to its own underground gas tanks, to prevent shortages in the winter.

The European Union earlier aired concerns about the level of gas reserves in Ukraine, but Ukraine has assured its partners last week it had been making greater progress to solve the issue.

Ukraine needs at least 24 billion cu m of gas in tanks to survive the winter and ensure that gas supplies from Russia to the E.U. continue without disruption.

Naftogaz reported last week that 24.3 billion cu m of gas was already stored in Ukraine as of Oct. 1, but said it planned to further boost the stocks to 25 billion as of Oct. 15, when the high demand season begins.

Ukraine moved 7.5 billion cu m of gas into its storage facilities in August-September, a record amount of gas shipped to the tanks within two months over the past 15 years, Naftogaz said.

Most of the gas stored in tanks is apparently owned by RosUkrEnergo, since Naftogaz has been facing up to $1.5 billion in losses this year, which would prevent the company from buying extra gas, analysts said. (nr/ez)