President Vladimir Putin kicked off a new exercise of Russia’s nuclear forces on Tuesday at a critical point in the Ukraine war, the second such drill that Moscow has held in two weeks.The 2-1/2-year-old war is entering what Russian officials say is its most dangerous phase as Russian forces are advancing in eastern Ukraine and the West considers how to shore up Ukraine.Russia has been signaling for weeks to the West that Moscow will respond if the United States and its allies help Ukraine fire longer-range missiles deep into Russia, while NATO says that North Korea has sent troops to western Russia.For all the latest headlines follow our Google News channel online or via the app.“We will work out the actions of officials to control the use of nuclear weapons with practical launches of ballistic and cruise missiles,” Putin was shown saying in a video clip announcing the drill.In video released by the Kremlin, Putin said using nuclear weapons would be an “extremely exceptional measure”