MOSCOW, April 29 (Reuters) - Russia on Saturday promised it would respond harshly to what it said was Poland's illegal seizure of its embassy school in Warsaw, an act it called a flagrant violation of the Vienna Convention on diplomatic relations. "We regard this latest hostile act by the Polish authorities as a blatant violation of the 1961 Vienna Convention on Diplomatic Relations and as an encroachment on Russian diplomatic property in Poland," the ministry said. See here for a complete list of exchanges and delays