BRUSSELS, Jan. 1 (Xinhua) -- The European Union (EU) on Thursday urged Russia and Ukraine to continue talks over their gas delivery dispute which could affect European supplies.

    "All existing commitments to supply and transit must be honored," Czech Deputy Prime Minister Alexandr Vondra, whose country holds the current EU presidency, said in a joint statement with the European Commission.

    Vondra said the EU regretted that no solution has been reached in the dispute between Russian natural gas giant Gazprom and Ukraine's gas company Naftogaz.

    Russia cut off natural gas supplies to Ukraine earlier Thursday after the two sides failed to reach an agreement on a contract dispute, arousing concerns that supplies to Europe might be disrupted because the EU receives one fifth of its natural gas through pipelines that cross Ukraine.

    Meanwhile, a joint statement signed by Ukrainian President Viktor Yushchenko and Prime Minister Yulia Tymoshenko made public early Thursday said that the country has asked the EU to mediate the dispute and promised supplies to Europe would continue "uninterrupted."

    The EU called for Russia and Ukraine to continue negotiations and rapidly reach an outcome so that supplies to Europe are not affected.

    "The EU believes that we can count on assurances given that gas supplies to the EU will be unaffected, as a demonstration of the reliability of its gas suppliers," said Andris Piebalgs, the EU commissioner for energy.