The prince earned fame as the architect of the Potemkin village, a town of brightly painted facades and happy people erected to deceive visiting officials and dignitaries. Critics have accused Mr. Putin of employing a similar sleight of hand in the invasion of Crimea and the supposedly spontaneous pro-Russian uprising in eastern Ukraine.

On Thursday, Mr. Putin repeated his assertion that he felt an obligation to protect ethnic Russians in eastern Ukraine, where they are a large minority of the population. “We must do everything to help these people to protect their rights and independently determine their own destiny,” he said.

“The question is to ensure the rights and interests of the Russian southeast,” he added. “It’s New Russia. Kharkiv, Luhansk, Donetsk, Odessa were not part of Ukraine in czarist times; they were transferred in 1920. Why? God knows. Then, for various reasons, these areas were gone, and the people stayed there. We need to encourage them to find a solution.”