The United States has not observed any signs indicating that Russia is preparing for a nuclear strike against Ukraine following new threats from dictator Vladimir Putin, reports Reuters. An unnamed American official told the news agency that Putin’s recent outburst likely reaffirmed Russia’s nuclear doctrine, under which it would use nuclear weapons “if their sovereignty is threatened.” “We have not seen any reason to adjust our own nuclear posture, nor any indications that Russia is preparing to use a nuclear weapon in Ukraine,” he noted. Putin’s remarks Russian dictator Vladimir Putin once a…