In contemporary international law, the national territory, including airspace and territorial sea, the Government and the people within its borders, makes the content of the state as subject of international law. Fulfilment of supreme and indivisible state authority within its territorial borders is an integral part of the state sovereignty.
Sphere of the state’s territorial supremacy is defined by its borders. The borders constitute state territory. The domestic laws establish legal regime in the border regions, such as the regime of guarding the border, regulations and conditions of entry / exit and residence in the border areas.
In accordance with the Constitution of Ukraine and relevant international laws, Autonomous Republic of Crimea is an integral part of Ukraine and is one of the administrative-territorial units of the UkrainianState.
Thus the decision of the Federation Council of the Federal Assembly of the Russian Federation on use of armed forces in the territory of independent sovereign state of Ukraine seriously contradicts international law.
Modern international law recognizes as legitimate only territorial changes that occur on a voluntary and equal basis, strictly in accordance with the provisions of consequent international agreement, subject to the sovereign will of local population, ethnic composition, economic community and the historical rights of all parties concerned.
Plebiscite is an important mean of peaceful resolution of territorial disputes. However, its application is possible only after the agreement is reached between the parties involved on cessation of armed hostilities, on armistice with any means under the Article 33 of the UN Charter. The plebiscite solving the territorial dispute could take place only by the consent of all parties involved.
Plebiscite receives its legal binding mainly in international treaties and resolutions of international organizations. Plebiscite is used while ensuring self-determination by people and nations, as well as their territorial settlement.
In this context, the actions of the Russian side should be classified as an act of annexation – forcible acquisition of a specific territory (Crimean peninsula).
Under the UN Charter (paragraph 4, Article 2) violent change of the territorial integrity is negligible and has no legal consequences. In addition, such actions should be treated as attempt to start an armed conflict, which is a violation of international law, since the latter prohibits the use or threat of force (except of self-defence) and obliges states to resolve all disputes solely by peaceful means.