Retired American general and former head of the CIA, David Petraeus, believes that in the event of Russia's use of nuclear weapons, the United States and its NATO allies should disable all conventional forces of the Russian Federation on the battlefield in Ukraine and Crimea.

 He said this on ABC News.

 Putin will lose despite "significant" but "desperate" steps in the war, Petraeus said.

 "President [Volodymyr] Zelenskiy and Ukraine mobilized much better than Russia. Ukraine recruited, trained, equipped, organized and deployed forces incomparably better than Russia," he noted.

 "No annexation, no amount of even veiled nuclear threats can get him out of this situation," the ex-CIA chief emphasized.

 Asked if Russia could win a war with Ukraine, Petraeus said he didn't see how: "They can't. There's nothing he [Putin] can do at this stage."

 "He will continue to lose on the battlefield," he said.

 Putin's speech on Friday, in which he announced the annexation of parts of Ukraine, was designed to undermine Europe's resolve to challenge Russia, which is the continent's main energy supplier, Petraeus said.

 "Europe is waiting for a hard winter. The flow of natural gas will be greatly reduced, but they will get through it, and I don't think they will break in the matter of supporting Ukraine," the general believes.

 "Everything could get worse for Putin and for Russia. And even using tactical nuclear weapons on the battlefield won't change that at all," Petraeus said.

 In response, he said, the US and its NATO allies could "disable all Russian conventional forces that we can see and identify on the battlefield" in Ukraine, in Crimea, which Russia annexed in 2014, and on ships in Black Sea.

 "This cannot go unanswered. But it will not be a war - there will be no nuclear weapons for nuclear weapons. Nobody wants to enter into a nuclear escalation. But it must be shown that this cannot be accepted in any way," Petraeus said.