By Daria Sito-SucicSARAJEVO (Reuters) - Poland and Ukraine on Thursday called for international sanctions against Russia's nuclear energy sector, saying they feared their neighbour may hurt energy security and economies in Europe if attacks on Ukrainian power facilities continue. Last week, the European Union adopted the tenth package of sanctions targeting Russia, but did not include its nuclear energy sector because of opposition from some EU member states. Russia formally suspended its participation in the New START nuclear arms control treaty on Tuesday, blaming Washington of using it to help Ukraine attack Russian strategic sites