Three of the sources, familiar with discussions in Putin's entourage, said the veteran Russian leader had expressed frustration to a small group of advisers about what he views as Western-backed attempts to stymie negotiations and Ukrainian President Volodymyr Zelenskiy's decision to rule out talks.

"Putin can fight for as long as it takes, but Putin is also ready for a ceasefire – to freeze the war," said another of the four, a senior Russian source who has worked with Putin and has knowledge of top level conversations in the Kremlin.

He, like the others cited in this story, spoke on condition of anonymity given the matter's sensitivity.

For this account, Reuters spoke to a total of five people who work with or have worked with Putin at a senior level in the political and business worlds. The fifth source did not comment on freezing the war at the current frontlines.

Putin's spokesman Dmitry Peskov, in response to a request for comment, said the Kremlin chief had repeatedly made clear Russia was open to dialogue to achieve its goals, saying the country did not want “eternal war.”

Ukraine's foreign and defence ministries did not respond to questions.

The appointment last week of economist Andrei Belousov as Russia's defence minister was seen by some Western military and political analysts as placing the Russian economy on a permanent war footing in order to win a protracted conflict.

It followed sustained battlefield pressure and territorial advances by Russia in recent weeks.

However, the sources said that Putin, re-elected in March for a new six-year term, would rather use Russia's current momentum to put the war behind him. They did not directly comment on the new defence minister.

Based on their knowledge of conversations in the upper ranks of the Kremlin, two of the sources said Putin was of the view that gains in the war so far were enough to sell a victory to the Russian people.

Europe's biggest ground conflict since World War Two has cost tens of thousands of lives on both sides and led to sweeping Western sanctions on Russia's economy.

Three sources said Putin understood any dramatic new advances would require another nationwide mobilisation, which he didn't want, with one source, who knows the Russian president, saying his popularity dipped after the first mobilisation in September 2022.

The national call up spooked part of the population in Russia, triggering hundreds of thousands of draft age men to leave the country. Polls showed Putin’s popularity falling by several points.

Peskov said Russia had no need for mobilisation and was instead recruiting volunteer contractors to the armed forces.

The prospect of a ceasefire, or even peace talks, currently seems remote.

Zelenskiy has repeatedly said peace on Putin's terms is a non-starter. He has vowed to retake lost territory, including Crimea, which Russia annexed in 2014. He signed a decree in 2022 that formally declared any talks with Putin "impossible."

One of the sources predicted no agreement could happen while Zelenskiy was in power, unless Russia bypassed him and struck a deal with Washington. However, U.S. Secretary of State Antony Blinken, speaking in Kyiv last week, told reporters he did not believe Putin was interested in serious negotiations.

SWISS TALKS

Ukraine is preparing for talks hosted by Switzerland next month aimed at unifying international opinion on how to end the war. The talks were convened at the initiative of Zelenskiy who has said Putin should not attend. Switzerland has not invited Russia.

Moscow has said the talks are not credible without it being there. Ukraine and Switzerland want Russian allies including China to attend.

Speaking in China on May 17, Putin said Ukraine may use the Swiss talks to get a broader group of countries to back Zelenskiy’s demand for a total Russian withdrawal, which Putin said would be an imposed condition rather than a serious peace negotiation.

The Swiss foreign ministry did not immediately respond to a request for comment.

"We are ready for discussion. We never refused," Putin said in China.

The Kremlin says it does not comment on the progress of what it calls its special military operation in Ukraine, but has repeatedly said Moscow is open to the idea of talks based on "the new realities on the ground."

In response to questions for this story, a U.S. State Department spokesperson said any initiative for peace must respect Ukraine’s “territorial integrity, within its internationally recognised borders” and described Russia as the sole obstacle to peace in Ukraine.

“The Kremlin has yet to demonstrate any meaningful interest in ending its war, quite the opposite,” the spokesperson said.

In the past, Kyiv has dismissed Russia's purported readiness to talk as an attempt to shift the blame onto it for the war.

Kyiv says Putin, whose team repeatedly denied he was planning a war before invading Ukraine in 2022, cannot be trusted to honour any deal.

Both Russia and Ukraine have also said they fear the other side would use any ceasefire to re-arm.

Kyiv and its Western backers are banking on a $61 billion U.S. aid package and additional European military aid to reverse what Zelenskiy described to Reuters this week as "one of the most difficult moments" of the full scale war.

As well as shortages of ammunition after U.S. delays in approving the package, Ukraine has admitted it is struggling to recruit enough troops and last month lowered the age for men who can be drafted to 25 from 27.

TERRITORY

Putin's insistence on locking in any battlefield gains in a deal is non-negotiable, all of the sources suggested.

Putin would, however, be ready to settle for what land he has now and freeze the conflict at the current front lines, four of the sources said.

"Putin will say that we won, that NATO attacked us and we kept our sovereignty, that we have a land corridor to Crimea, which is true," one of them said, giving their own analysis.

Freezing the conflict along current lines would leave Russia in possession of substantial chunks of four Ukrainian regions he formally incorporated into Russia in September 2022, but without full control of any of them.

Such an arrangement would fall short of the goals Moscow set for itself at the time, when it said the four of Ukraine's regions - Donetsk, Luhansk, Zaporizhzhia and Kherson - now belonged to it in their entirety.

Peskov said that there could be no question of handing back the four regions which were now permanently part of Russia according to its own constitution.

Another factor playing into the Kremlin chief's view that the war should end is that the longer it drags on, the more battle-hardened veterans return to Russia, dissatisfied with post-war job and income prospects, potentially creating tensions in society, said one of the sources, who has worked with Putin.

'RUSSIA WILL PUSH FURTHER'

In February, three Russian sources told Reuters the United States rejected a previous Putin suggestion of a ceasefire to freeze the war.

In the absence of a ceasefire, Putin wants to take as much territory as possible to ratchet up pressure on Ukraine while seeking to exploit unexpected opportunities to acquire more, three of the sources said.

Russian forces control around 18% of Ukraine and this month thrust into the northeastern region of Kharkiv.

Putin is counting on Russia's large population compared to Ukraine to sustain superior manpower even without a mobilisation, bolstered by unusually generous pay packets for those who sign up.

"Russia will push further," the source who has worked with Putin said.

Putin will slowly conquer territories until Zelenskiy comes up with an offer to stop, the person said, saying the Russian leader had expressed the view to aides that the West would not provide enough weapons, sapping Ukraine's morale.

U.S. and European leaders have said they will stand by Ukraine until its security sovereignty is guaranteed. NATO countries and allies say they are trying to accelerate deliveries of weapons.

“Russia could end the war at any time by withdrawing its forces from Ukraine, instead of continuing to launch brutal attacks against Ukraine’s cities, ports, and people every day,” the State Department said in response to a question about weapons supplies.

All five sources said Putin had told advisers he had no designs on NATO territory, reflecting his public comments on the matter. Two of the sources cited Russian concerns about the growing danger of escalation with the West, including nuclear escalation, over the Ukraine standoff.

The State Department said the United States had not adjusted its nuclear posture, nor seen any sign that Russia was preparing to use a nuclear weapon.

“We continue to monitor the strategic environment and remain ready,” the spokesperson said.