BERLIN, Jan 27 (Reuters) - The chief executive of Ukrainian state energy firm Naftogaz on Friday said the European Union should block the Russia-led Nord Stream-2 gas project as it would give the Kremlin geopolitical and financial leverage over Germany, Poland and Slovakia.

    Russia's Gazprom <GAZP.MM> and its European partners agreed the Nord Stream-2 project in 2015, but critics say it could limit supply routes and the energy security of the European Union, which gets a third of its gas from Russia.

    "We are urging our European partners to try not to look at immediate consequences but one step further - what will happen a bit later after Nord Stream-2 is launched," Naftogaz chief     Andriy Kobolev told Reuters in an interview.

    Kobolev said the planned underwater gas pipeline's annual capacity of 55 billion cubic metres would result in an equivalent drop in volumes that currently transit via Ukraine and Poland, killing those supply routes.

    "I don't believe that has anything to do with diversification or increase of security of supply. It means increase of the dominant position of Gazprom in this part of Europe," he said.

    "There is an easy legal way (to stop it). EU should apply same logic like with South stream, apply the Third Energy Package, then you can't build Nordstream 2. Legal arguments have been overlooked so far."

    The EU's Third Energy Package, sets regulations that seek to prevent energy suppliers from dominating infrastructure.

    Ukraine has been among the staunchest opponents of the Nord Stream-2. Around a third of the gas the EU imports from Gazprom is pumped via Ukraine and the new pipeline would sideline the country as a gas transit route, depriving it of billions of dollars in fees.

    Kobolev said European countries needed to be careful of making themselves more dependent on Russia.

    "When there will be no Ukrainian route and Germany will be left with two Nordstreams then Gazprom can use this for different ways of blackmail: higher prices, it could be geopolitical pressure, it could be blackmail of other neighbours of Russia like Poland, Slovakia," he said.

    Ukraine is locked in its own long-running gas pricing feud with Russia. Gazprom and Naftogaz have taken their dispute over contracts running through 2019 to an international arbitration court in Stockholm, each claiming about $30 billion.

    Kobolev said Russia had initiated the row to make Ukraine appear as an unreliable transit route and persuade Europe of the benefits of an alternative pipeline.

    "The real reason is that Russians are using this as a tool and weapon to push their ideas," he said.

    Kobolev also said that Gazprom was not fulfilling its contractual obligation under the Ukraine transit contract by providing gas at a lower pressure than required, resulting in less reliable flows to Europe.

    "Gazprom's desire to create conflict in order to promote circumventing routes or to try and show Ukraine is unreliable has always been their tactic, so I cannot exclude the possibility of a gas crisis this winter as well," he said.