An ally of President Vladimir Putin has warned that Russia has the weapons to destroy any enemy, including the United States, if its own existence is threatened, accusing Washington of underestimating Moscow's nuclear might. The comments from Nikolai Patrushev, the influential secretary of Russia's Security Council, are the latest from a senior Russian official to raise the spectre of a nuclear showdown between the world's two largest nuclear powers, something Moscow says it wants to avoid.