KYIV/MOSCOW (Reuters) -Talks between Russian and Ukrainian officials began on the Belarusian border on Monday, as Russia faced deepening economic isolation four days after invading Ukraine in the biggest assault on a European state since World War Two. Russian forces seized two small cities in southeastern Ukraine and the area around a nuclear power plant, the Interfax news agency said on Monday, but ran into stiff resistance elsewhere. Talks began with the aim of an immediate ceasefire and the withdrawal of Russian forces, the Ukrainian president’s office said, after a Russian advance that ha…