By Robin Emmott and Jan Strupczewski BRUSSELS (Reuters) - The European Union was set to press U.S. President Barack Obama on Wednesday to help reduce Europe's reliance on Russian energy by exporting U.S. natural gas, as relations with Moscow chill over its intervention in Ukraine. Obama began his visit to Belgium by visiting the Flanders Field American war cemetery, visiting the graves of some of the 368 U.S. service members, most killed during World War One. His visit and the symbolism of transatlantic unity had added resonance at a time when tensions in Europe are running high because of Russia's military occupation and annexation of Ukraine's Crimea region. We must commit perennially to peace, which binds us across oceans," Obama said.