President Biden's decision to allow Ukraine to fire U.S.-made and supplied missiles deeper into Russia — a major policy shift announced over the weekend after months of intense lobbying by Kyiv — has drawn a furious response from Moscow.

Vladimir Putin ratcheted up the threat of a nuclear attack if US-supplied longer range missiles are fired by Ukraine into Russia. The Russian president on Tuesday signed a revised nuclear doctrine declaring that a conventional attack on Russia by any nation that is supported by a nuclear power will be considered a joint attack on his country.