On 1 July 1968, Mikhail Nikolayevich Smirnovsky, Soviet Ambassador to the United Kingdom, signs the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). Under this multilateral treaty, the five nuclear weapon states — the United States, USSR, United Kingdom, China and France — agree not to transfer military nuclear technology to other states. On 5 March 1970, after ratification by the depositary governments, the treaty comes into force for 25 years. On 11 May 1995, following a conference at the United Nations Headquarters in New York that lasts for almost a month, the representatives of more than 180 countries decide that the NTP should continue in force indefinitely.