Worried by a drop in Russian gas volumes being transited via Ukraine and Slovakia, Kiev has asked the EU to discuss the issue with Moscow.

According to Ukraine’s Energy Minister Yuri Prodan, the decline in gas volumes is serious and a cause of concern for the government in Kiev.

The reduction “can have implications for the energy security of Ukraine and countries of the European Union,” ITAR-TASS quoted Prodan as saying in a letter to European Commission Vice-President Guenther Oettinger.

The European Union is seeking gas talks with Russia and Ukraine to avert disruptions in deliveries during winter months. Trilateral talks have been tentatively scheduled for September 22.

In June, Russia’s Gazprom halted supplies to Ukraine over growing debts and a gas pricing dispute. EU members Poland and Slovakia, which have been supplying gas to Ukraine, say Gazprom is delivering less than requested.

Gazprom denies those claims, saying it is  fulfilling its contractual obligations but cannot meet the requests for additional volumes as Russia itself is preparing for the coming winter.

Gazprom spokesman Sergei Kupriyanov said on Monday that European customers have been receiving smaller gas volumes from Russia than they had requested because Russia was pumping gas into its own storage.

European supplies will depend on Gazprom’s winter preparation in Russia, Kupriyanov said.

He added that gas transit via Ukraine to Slovakia had also fallen because part of volumes have been returned to Yamal-Europe gas pipeline, which has resumed operations following repairs.

Gazprom needs 45 days to increase domestic gas inventories by about 8.5 billion cubic meters (bcm)to 72 bcm, CEO Alexey Miller told Russian President Vladimir Putin in Moscow on Wednesday.

The company also has 3.8 bcm in European storage, and plans to pump additional 5 bcm, Miller added.