"The European Commission has opened formal proceedings to investigate whether Gazprom, the Russian producer and supplier of natural gas, might be hindering competition in central and eastern European gas markets, in breach of EU anti-trust rules," the European Union executive said in a statement.

The Brussels-based competition watchdog said it opened the formal legal probe based on "concerns that Gazprom may be abusing its dominant market position in upstream gas supply markets."

It cited three areas for investigation -- the possible division of gas markets "by hindering the free flow of gas across (EU) member states;" the possible prevention of gas-supply diversification; and fears that Gazprom may have "imposed unfair prices on its customers by linking the price of gas to oil prices."

The opening of proceedings, which the Commission stressed does not prejudge the outcome, means that it "will treat the case as a matter of priority."

The move follows September 2011 inspections at gas company premises and comes amid recurrent concerns that lower gas supplies from Russia could spell potentially higher prices for consumers.

The EU imports 80 percent of its gas needs, one third of which comes from Russia, and has frequently found itself at loggerheads with Moscow over energy supply.