Veteran US diplomat Henry Kissinger said the time is approaching for a negotiated peace in Ukraine to reduce the risk of another devastating world war, but the Kyiv government dismissed his comments as amounting to "appeasing the aggressor" and said there could be no deal involving ceding territory. 

Kissinger, 99, and an architect of the Cold War policy of detente towards the Soviet Union as secretary of state under Republican presidents Richard Nixon and Gerald Ford, has met Russia's Vladimir Putin multiple times since he first became president in 2000. 

There is no end in sight to the conflict sparked by Putin's Feb. 24 invasion of Ukraine, which has killed tens of thousands of people and driven millions from their homes. Russia now controls around a fifth of Ukraine. 

The Kremlin says Kyiv must acknowledge Moscow's annexation of southern and eastern regions. Ukraine says every Russian soldier must leave its territory, including Crimea, which Russia annexed in 2014. Kyiv applied to join NATO after Moscow announced the later annexations in September. 

"The time is approaching to build on the strategic changes which have already been accomplished and to integrate them into a new structure towards achieving peace through negotiation," Kissinger wrote in The Spectator magazine. 

"A peace process should link Ukraine to NATO, however expressed. The alternative of neutrality is no longer meaningful," Kissinger wrote. 

Kissinger said that in May he had proposed a ceasefire under which Russia would withdraw to the front lines before the February invasion but Crimea would be the subject of "negotiation". 

The conflict in eastern Ukraine began in 2014 after a pro-Russian president was toppled in Ukraine and Russia annexed Crimea, with Russian-backed separatists fighting Ukraine's armed forces in eastern Ukraine. 

"Mr. Kissinger still has not understood anything ... neither the nature of this war, nor its impact on the world order," Ukrainian presidential aide Mykhailo Podolyak said on Telegram. 

"The prescription that the ex-Secretary of State calls for, but is afraid to say out loud, is simple: appease the aggressor by sacrificing parts of Ukraine with guarantees of non-aggression against the other states of Eastern Europe." 

He added, "All supporters of simple solutions should remember the obvious: any agreement with the devil - a bad peace at the expense of Ukrainian territories - will be a victory for Putin and a recipe for success for autocrats around the world." 

Kremlin officials were not available for comment late on Sunday. 

Aaron David Miller, a senior fellow at the Carnegie Endowment think tank, also dismissed Kissinger's proposal, saying in a Twitter post: 

"Henry Kissinger calls for cease-fire along borders pre-war 2/24 with Russia disgorging its conquests and negotiations on territory seized in 2014. What Kissinger doesn’t allow for are politics on both sides making this idea impossible now, maybe never." 

CIA Director William Burns said in an interview published on Saturday that while most conflicts end in negotiation, the CIA's assessment was Russia was not serious yet about a real negotiation to end the war. 

Putin casts what he calls Russia's "special military operation" as a watershed moment when Russia finally stood up to a Western bloc, led by the United States, seeking to capitalize on the 1991 fall of the Soviet Union by destroying Russia. 

Ukraine and the West say Putin has no justification for what they say is an imperial-style war of occupation. 

Kissinger warned that desires to render Russia "impotent", or even seek the dissolution of Russia, could unleash chaos. Neither Ukraine nor any Western state has advocated either path.