Russian military operation. Numerous media reports and statements by the Ukrainian and foreign governments noted the identity of the unmarked troops as Russian soldiers, but Russian officials concealed the identity of their forces, claiming they were local "self-defence" units over whom they had no authority. As late as 17 April, Russian foreign minister Sergey Lavrov said that there were no "excessive Russian troops" in Ukraine. At the same press conference, Putin said of the peninsula that "only citizens themselves, in conditions of free expression of will and their security can determine their future". Putin later acknowledged that he had ordered "work to bring Crimea back into Russia" as early as February. He also acknowledged that in early March there were "secret opinion polls" held in Crimea, which, according to him, reported overwhelming popular support for Crimea's incorporation into Russia. Russia eventually admitted its troops' presence. Defence Minister Sergey Shoygu said the country's military actions in Crimea were undertaken by forces of the Black Sea Fleet and were justified by "threat to lives of Crimean civilians" and danger of "takeover of Russian military infrastructure by extremists". Ukraine complained that by increasing its troop presence in Crimea, Russia violated the agreement under which it headquartered its Black Sea Fleet in Sevastopol and violated the country's sovereignty. The United States and United Kingdom accused Russia of breaking the terms of the Budapest Memorandum on Security Assurances, by which Russia, the US, and the UK had reaffirmed their obligation to refrain from the threat or use of force against the territorial integrity or political independence of Ukraine. The Russian government said the Budapest Memorandum did not apply due to "circumstances resulting from the action of internal political or socio-economic factors". In March 2015, retired Russian Admiral stated that according to his information the Russian troop deployment in Crimea included six helicopter landings and three landings of an IL-76 with 500 people. Legal issues The obligations between Russia and Ukraine with regard to territorial integrity and the prohibition of the use of force are laid down in a number of multilateral or bilateral agreements to which Russia and Ukraine are signatories. Vladimir Putin said that Russian troops in the Crimean peninsula were aimed "to ensure proper conditions for the people of Crimea to be able to freely express their will," whilst Ukraine and other nations argue that such intervention is a violation of Ukraine's sovereignty.