(Reuters) – Ukraine has defied Russia’s demand for soldiers to lay down arms in Mariupol, where civilians are besieged in a city being laid to waste by bombardment. Russia’s almost month-old assault on Ukraine has stalled along most fronts, failing to seize any major city or topple the government. But shelling and missiles are causing devastation. FIGHTING * In the capital Kyiv, shells hit a shopping centre, killing at least eight people. * Authorities in Odesa accused Russian of a strike on residential buildings, the first such attack on the Ukrainian Black Sea port. CIVILIANS * Horror and be…