U.N. Secretary-General Ban Ki-moon warned international leaders Monday that the Ukraine crisis could have profound implications for the integrity of a global treaty designed to prevent the spread of nuclear weapons.
Ukraine gave up its Soviet-era nuclear arsenal under the 1994 Budapest Memorandum, which it signed together with Britain, the United States and Russia. It provided guarantees of Ukraine's sovereignty in exchange for a commitment, since fulfilled, to give up the country's nuclear weapons.
Russia, however, has seized and annexed Ukraine's Russian-majority region of Crimea following the fall in February of Ukraine's pro-Russian president after months of mass protests.