* European Commission says seeking to diversify supplies
* Says Russia's existing pipeline capacity underused (Adds context, detail)
BRUSSELS, June 19 (Reuters) - A planned expansion of theNord Stream pipeline that delivers Russian gas to Germany mustcomply with EU laws, the European Commission said on Friday,adding it was working to maintain Ukraine's role as an importanttransit country.
Russia's Gazprom said on Thursday that Royal DutchShell and its long-time gas buyers in Europe -Germany's E.ON and Austria's OMV - hadagreed to build two new Nord Stream gas pipelines under theBaltic Sea to Germany.
The announcement runs counter to Commission efforts to workwith suppliers other than Russia, and to create a robust energyunion based on closer collaboration between the 28 member statesand sharing of available supplies.
Russia provides around a third of the EU's energy.
In its first public response to Thursday's news, theCommission said it would be vigilant about enforcing EU law thatprevents any one supplier dominating the market and would keepworking with Ukraine as "a major reliable transit country".
"The European Commission recalls that new pipelines must bebuilt in full compliance with EU legislation and will bevigilant about the rigorous application of EU law notably in thefield of energy, internal market and competition," a statementsaid.
The statement reiterated the Commission's commitment toseeking diverse gas suppliers, including more use of liquefiednatural gas (LNG).
Although European domestic gas production is expected tofall, so far only around 57 percent of Russian capacity to theEU is used, the EU executive said.
While the European Union has been seeking to curb itsdependence on Russian energy, Russia has been working todiversify its supply routes.
The 55 billion cubic metre per year expansion of Nord Streamis in addition to Gazprom's planned Turkish Stream project todeliver 47 bcm to Europe via Turkey.
Moscow has said the ultimate aim is to cease relying onUkraine, which the Commission said was the route for roughlyhalf of the Russian gas shipped to the EU. (Reporting by Barbara Lewis; Editing by Dale Hudson and Foo YunChee)
