With rare exception, diplomatic missions are NOT the sovereign soil of the represented nation. The host nation has various obligations to the mission (such as not entering it w/o the approval of the represented nation, diplomatic immunity, etc.) but these obligations exist because the host nation signed the Vienna Convention on Diplomatic Relations, not because the represented nation has sovereignty on the soil of the mission. If a host nation were to enter a diplomatic mission without permission of the represented nation, they are violating the Vienna Convention on Diplomatic Relations, but they are not violating sovereignty. Just for the record.