Russia has accused the European Union of discriminating against gas and electricity providers from outside the bloc in violation of international rules, the World Trade Organization said Thursday.
"The Russian Federation has notified the WTO Secretariat on April 30 of a request for consultations with the European Union over measures applied by the EU relating to the so-called 'Third Energy Package'," the organisation said.
Russian giant Gazprom has previously challenged those regulations, which ban the same company from owning both pipelines and distribution networks -- seen as a move to boost competition and ease Europe's dependence on the state-controlled firm.
Russia accounts for about a quarter of all EU gas supplies and is the dominant or sole supplier to some members of the 28-nation bloc, notably ex-communist countries.
Moscow charges that the EU rules discriminate against third countries involved in the production, supply and transmission of natural gas, and that they breach a range of international trade agreements, the WTO said.
The move comes amid heightened tensions over the Ukraine crisis, with Gazprom warning this week that new sanctions from the EU and others against Russia could leave Europe without crucial gas supplies.
Talks were due to take place Friday in Warsaw between the EU, Russia and Kiev over the gas dispute.
Russia has threatened to cut supplies to Ukraine over a $3.5-billion (2.5-billion-euro) unpaid gas bill, raising concerns of a repeat of 2009 when supplies to Europe that transit through the former Soviet republic were badly disrupted.
But Russia's chief WTO negotiator Maxime Medvedkov insisted Wednesday its claim before the body had nothing to do with the Ukraine crisis.
The EU energy sector regulations "create a serious obstacle to securing a solid supply of Russian gas to the European Union," he told the Interfax news agency, maintaining that Moscow for years had been attempting to settle the matter bilaterally.
"Our goal is not to sue Brussels just for the sake of it. We want to ensure a predictable environment for exports to the EU, in accordance with WTO rules," he said.
Moscow's request for WTO consultations marks the first step in a complex settlement process which can last several years.
The consultations, which allow the parties to seek a settlement without resorting to litigation, should begin within a month and cannot continue for more than 60 days after the request is received.
If they fail, Russia can ask the WTO's Dispute Settlement Body to review the dispute.
Wednesday's request marks the second complaint 2012 WTO entrant Russia has filed against the EU since December, when it claimed the bloc was putting Russian steel and fertiliser companies at a disadvantage through unfair anti-dumping tariffs.