Analysis-What is Russia's policy on tactical nuclear weapons?

FILE PHOTO: A frame taken from a Russian television broadcast on December 31 shows a set of briefcases which contain the codes to launch Russia's armoury of nuclear missiles. Russian President Boris Yeltsin stunnned his own people and the world when he resigned on Friday and handed over his duties, including the briefcase, [to Prime Minister Vladimir Putin during thier meeting in the Kremlin./File Photo

LONDON (Reuters) - The United States has said the world faces the gravest nuclear danger since the 1962 Cuban Missile Crisis because of remarks by Russian leader Vladimir Putin during the Ukraine conflict, but Moscow says its position has been misinterpreted.

Kyiv and its Western allies fear tactical nuclear weapons could be used in battle after Putin and others warned Russia was prepared to use all its vast arsenal in defence.