President Vladimir Putin's conditions for ending the war in Ukraine include a demand that Western leaders pledge in writing to stop enlarging NATO eastwards and lift a chunk of sanctions on Russia, according to three Russian sources with knowledge of the negotiations.

U.S. President Donald Trump has repeatedly said he wants to end the deadliest European conflict since World War Two and has shown increasing frustration with Putin in recent days, warning on Tuesday the Russian leader was "playing with fire" by refusing to engage in ceasefire talks with Kyiv as his forces made gains on the battlefield.

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After speaking to Trump for more than two hours last week, Putin said that he had agreed to work with Ukraine on a memorandum that would establish the contours of a peace accord, including the timing of a ceasefire. Russia says it is currently drafting its version of the memorandum and cannot estimate how long that will take.

Kyiv and European governments have accused Moscow of stalling while its troops advance in eastern Ukraine.

"Putin is ready to make peace but not at any price," said one senior Russian source with knowledge of top-level Kremlin thinking, who spoke on condition of anonymity.

The three Russian sources said Putin wants a "written" pledge by major Western powers not to enlarge the U.S.-led NATO alliance eastwards - shorthand for formally ruling out membership to Ukraine, Georgia and Moldova and other former Soviet republics.

Russia also wants Ukraine to be neutral, some Western sanctions lifted, a resolution of the issue of frozen Russian sovereign assets in the West, and protection for Russian speakers in Ukraine, the three sources said.

The first source said that, if Putin realizes he is unable to reach a peace deal on his own terms, he will seek to show the Ukrainians and the Europeans by military victories that "peace tomorrow will be even more painful".

The Kremlin did not respond to a request for comment on Reuters' reporting. Putin and Russian officials have repeatedly said any peace deal must address the "root causes" of the conflict - Russian shorthand for the issue of NATO enlargement and Western support for Ukraine.

Kyiv has repeatedly said that Russia should not be granted veto power over its aspirations to join the NATO alliance. Ukraine says it needs the West to give it a strong security guarantee with teeth to deter any future Russian attack.

President Volodymyr Zelenskiy's administration did not respond to a request for comment.

NATO has also in the past said that it will not change its "open door" policy just because Moscow demands it. A spokesperson for the 32-member alliance did not respond to Reuters' questions.

Putin ordered tens of thousands of troops into Ukraine in February 2022 after eight years of fighting in eastern Ukraine between Russian-backed separatists and Ukrainian troops.

Russia currently controls just under one fifth of the country. Though Russian advances have accelerated over the past year, the war is costing both Russia and Ukraine dearly in terms of casualties and military spending.

Reuters reported in January that Putin was growing concerned by the economic distortions in Russia's wartime economy, amid labour shortages and high interest rates imposed to curb inflation. The price of oil, the bedrock of Russia's economy, has declined steadily this year.

Trump, who prides himself on having friendly relations with Putin and has expressed his belief the Russian leader wants peace, has warned that Washington could impose further sanctions if Moscow delays efforts to find a settlement. Trump suggesting on social media on Sunday that Putin had "gone absolutely CRAZY" by unleashing a massive aerial attack on Ukraine last week.

The first source said that if Putin saw a tactical opportunity on the battlefield, he would push further into Ukraine - and that the Kremlin believed Russia could fight on for years no matter what sanctions and economic pain were imposed by the West.

A second source said that Putin was now less inclined to compromise on territory and was sticking to his public stance that he wanted the entirety of four regions in eastern Ukraine claimed by Russia.

"Putin has toughened his position," the second source said of the question of territory.

NATO ENLARGEMENT

As Trump and Putin joust in public over the outlook for peace in Ukraine, Reuters could not determine whether the intensification of the war and the toughening of positions heralds determination to reach a deal or the collapse of talks.

In June last year, Putin set out his opening terms for an immediate end to the war: Ukraine must drop its NATO ambitions and withdraw all of its troops from the entirety of the territory of four Ukrainian regions claimed and mostly controlled by Russia.

In addition to Crimea, which it annexed in 2014, Russia currently controls almost all of Luhansk, more than 70% of Donetsk, Zaporizhzhia and Kherson regions. It also occupies a sliver of the Kharkiv and Sumy regions, and is threatening Dnipropetrovsk.

Former U.S. President Joe Biden, Western European leaders and Ukraine cast the invasion as an imperial-style land grab and have repeatedly vowed to defeat Russian forces.

Putin casts the war as a watershed moment in Moscow's relations with the West which he says humiliated Russia after the Soviet Union fell in 1991 by enlarging NATO and encroaching on what he considers Moscow's sphere of influence.

At the 2008 Bucharest summit, NATO leaders agreed that Ukraine and Georgia would one day become members. Ukraine in 2019 amended its constitution committing to the path of full membership of NATO and the European Union.

Trump has said that previous U.S. support for Ukraine's NATO membership bid was a cause of the war, and has indicated that Ukraine will not get membership. The U.S. State Department did not respond to a request for comment for this story.

Putin, who rose to the top Kremlin job in 1999, has repeatedly returned to the issue of NATO enlargement, including in his most detailed remarks about a possible peace in 2024.

In 2021, just two months before the Russian invasion, Moscow proposed a draft agreement, opens new tab with NATO members that, under Article 6, would bind NATO to "refrain from any further enlargement of NATO, including the accession of Ukraine as well as other States." U.S. and NATO diplomats said at the time that Russia could not have a veto on expansion of the alliance.

Russia wants a pledge on NATO in writing because Putin thinks Moscow was misled by the United States after the 1989 fall of the Berlin Wall when U.S. Secretary of State James Baker assured Soviet leader Mikhail Gorbachev in 1990 that NATO would not expand eastwards, two of the sources said.

There was such a verbal promise, former Central Intelligence Agency Director Director William J. Burns said in his memoires, but it was never formalised - and it was made at a time when the collapse of the Soviet Union had not occurred.

NATO, founded in 1949 to provide security against the Soviet Union, says it poses no challenge to Russia - though its 2022 assessment of peace and security in the Euro-Atlantic area identified Russia as the most "significant and direct threat", opens new tab.

Russia's invasion of Ukraine that year prompted Finland to join NATO in 2023, followed by Sweden in 2024.

Western European leaders have repeatedly said that if Russia wins the Ukraine war, it could one day attack NATO itself - a step that would trigger a world war. Russia dismisses such claims as baseless scaremongering, but has also warned the war in Ukraine could escalate into a broader conflict.