Dmitry Medvedev also said Russia was prepared to hold talks with Ukrainian President Volodymyr Zelensky.
A top ally of Russian President Vladimir Putin said on Friday that Moscow would not stop its military campaign in Ukraine even if Kyiv formally renounced its aspirations to join NATO.
Former President Dmitry Medvedev, now deputy chairman of Russia's Security Council, also said in a French television interview that Russia was prepared to hold talks with Ukrainian President Volodymyr Zelenskiy subject to certain conditions.
Even before the February invasion, Moscow made clear Ukrainian membership of NATO was unacceptable to it.
"Renouncing its participation in the North Atlantic alliance is now vital, but it is already insufficient in order to establish peace," Medvedev told LCI television in quotes reported by Russian news agencies.
Russia, he said, would continue the campaign until its goals had been achieved. Putin says he wants to "denazify" Ukraine. Kyiv and the West say this is a baseless pretext for a war of conquest.
Russia and Ukraine held several rounds of talks after the invasion began, but they made no progress and there are few prospects for a resumption.
"This (talks) will depend on how events unfold. We were ready before to meet (Zelenskiy)," Medvedev said.
In his comments, he also said U.S. weapons already supplied to Ukraine -- like HIMARS multiple-rocket launchers - did not yet pose a substantial threat.
But that could change, he said, if U.S. sent weapons could hit targets at longer distances.
"It means that when this sort of missile flies 70 km, that is one thing," he said. "But when it's 300-400 km, that is another, now that would be a threat directly to the territory of the Russian Federation."
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