Belarusian opposition decries move as an attempt to blackmail the West as Ukraine steps up offensive

State Department spokesman blasts 'dangerous' comments by Russian leader, who hinted at use of tactical nukes, told Kremlin 'such a threat is rising'

Alarm in Washington as intelligence shows top generals examined various scenarios for a strike, officials tell NY Times -- but leader Putin was not involved

Kremlin watchers believe nuclear action is unlikely, but also note that brinkmanship could escalate even before a bomb is used

The Russian president has threatened to use battlefield nukes in Ukraine, but such a move would achieve little and could set in motion unstoppable full-scale nuclear war with West