WASHINGTON/LVIV, Ukraine (Reuters) – Ukraine must hold off Russia’s attack for the next seven to 10 days to deny Moscow claiming any sort of victory, said a senior government official, as more than 2 million refugees fled the biggest assault on a European country since World War Two. Vadym Denysenko, adviser to Ukraine’s interior minister, said Russia was desperate for at least some kind of victory, citing the cities of Mariupol or the capital Kyiv as the most likely targets. “They need at least some victory before they are forced into the final negotiations,” Denysenko wrote on Facebook. “The…