Russian scientists have developed “a small-scale heavy-duty nuclear energy unit,” Mr. Putin said, that can power a cruise missile so that it could achieve “basically an unlimited range.”

Such a technology could evade American defenses and alter the balance of power. But analysts were skeptical.

“If we’re talking about nuclear-armed cruise missiles, that’s a technological breakthrough and a gigantic achievement,” said Aleksandr M. Golts, an independent Russian military analyst. But, he added, “The question is, is this true?”

Mr. Putin said the nuclear cruise missile had been tested successfully late last year. But American officials said they believed it is not yet operational, despite Mr. Putin’s claims, and that it had crashed during testing in the Arctic.

The video shows a missile launching and then fades into an animation in which a cruise missile maneuvers around natural barriers, like mountains, as well as missile defense systems created to intercept it. “It is invincible against all existing and prospective missile defense and counter-air defense systems,” Mr. Putin claimed. At the end of the animation, the missile zeros in on Hawaii.