Russian energy giant Gazprom has switched to advanced payment mode for gas deliveries to Ukraine's Naftogaz, company officials have announced.

Gazprom has also filed a lawsuit at the Stockholm arbitration court, in an attempt to get back its gas debts.

The decision has been in force since 10:00 Moscow Time (06:00 GMT), a company message cited by ITAR-TASS agency shows.

Russia's energy concern has cited "chronic non-payment from Naftogaz Ukraine" as a reason for its move.

It has reminded that Naftogaz's debts amount to USD 4.458 B for November-December 2013 and April-May 2014.

An instalment of that sum worth USD 1.95 B was to be transferred by June 16, 06:00 GMT.

Russian Deputy Prime Minister Arkady Dvorkovich explained that advanced payment was introduced after a report submitted to President Vladimir Putin by Gazprom CEO Alexey Miller.

The latest developments follow the failure of Sunday's talks between Russian and Ukrainian officials moderated by EU Energy Commissioner Gunther Oettinger.

Gazprom and Naftogaz have sought a way out of a bitter gas dispute which broke after Moscow announced it was scrapping discounts for Kiev's supplies and introduced a 80% price hike in April this year.

With deliveries coming to a halt as the country refuses to pay under the current regime, some experts believe the situation carries a risk to Europe's deliveries, 15% of which are transported via Ukraine.

Gazprom spokesman Sergey Kuprianov however maintains that Ukraine has "an obligation" to allow passage to European gas and that customers to the west are to receive the full volume they are to be delivered under existing agreements.

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