U.S. called a "historic step" the day when Ukraine renounced nuclear weapons 20 years ago.
On this occasion, Deputy U.S. Department of State Spokesperson Marie Harf made the relevant  statement:

“On this day, 20 years ago, the presidents of Ukraine, the United States and the Russian Federation signed a trilateral statement that led to the removal of all nuclear weapons on Ukrainian territory. This statement laid the foundation for Ukraine’s accession to the Nuclear Non-Proliferation Treaty (NPT),” press release reads.

U.S. Department of State reminded that then “the three presidents committed to the transfer of all nuclear warheads out of Ukraine in exchange for compensation to Ukraine”, including the U.S. provision of substantial Nunn-Lugar Cooperative Threat Reduction assistance to cover the costs of safely and securely eliminating ICBMs, strategic bombers, ICBM silos and other nuclear infrastructure in Ukraine. 

“Presidents Clinton and Yeltsin further informed Ukrainian President Kravchuk that the United States and Russia were prepared to provide security assurances to Ukraine once Ukraine acceded to the NPT and the START I Treaty entered into force,” the statement says.

Marie Harf notes that “Ukraine’s historic action in 1994, and its further efforts over the past two decades, have helped ensure the NPT remains the cornerstone of the nuclear nonproliferation regime”.

“As we approach the 2015 NPT Review Conference, the United States looks to all States Parties to work together towards strengthening this critical treaty which has underpinned international security for nearly 45 years,” U.S. Department of State notes.

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