By Andrew Osborn

LONDON (Reuters) -Russia, like U.S. President Donald Trump, covets Ukraine's natural resources - and on the ground its forces are closing in on a giant lithium deposit.

Trump said this month he wants Kyiv to hand over large quantities of its critical minerals in return for U.S. military support, prompting Ukrainian President Volodymr Zelenskiy to declare: "Let's do a deal."

Yet as Washington and Moscow prepare for negotiations aimed at ending the three-year-old war, the reality is that it's Vladimir Putin who's taking increasing control of Ukraine's riches.

Russian forces, which have already seized a fifth of Ukraine including reserves of rare earths, are now little more than 4 miles from the Shevchenko lithium deposit and advancing on it from three different angles, according to open-source data from Ukrainian military blog Deep State.

Lithium is a coveted global resource because of its use in a host of industries and technologies from mobile phones to electric cars. Ukraine has reserves of about 500,000 tons, and Russia double that, according to U.S. government estimates.

Shevchenko is located in Donetsk, one of four Ukrainian regions that Moscow has claimed as its own territory, an annexation that Kyiv and Western powers say is illegal. It is one of the biggest lithium deposits in Ukraine and sits at a depth that would allow commercial mining.

"Given the current battlefield tempo, it's likely that the Russians will reach this area in the coming weeks," said Konrad Muzyka, director of the Rochan military consultancy in Poland, who has just returned from a research trip to Ukraine.

He said the seizure of Ukraine's mineral wealth, while not the main war aim, was among Russia's strategic goals.

"Ukrainian commanders I spoke to said that when they were looking in which direction and on which axis the Russians were attacking it was clear that their objective was also the capture of natural resources," he added.

Vladimir Ezhikov, a senior Russian-appointed official in Donetsk, has said that the mining division of Russia's state nuclear corporation Rosatom has shown an interest in the Shevchenko deposit, but that Russia's ministry of natural resources would hand out a mining licence when the time came.

"It's hard to predict when this will happen, as for now the deposit is in the 'grey zone' and there's no possibility of developing it due to military action," he told the local state news agency in January.

"This deposit will definitely find its licencee. There will definitely be investment and lithium mining, and we would certainly like to see processing done here too."

'RUSSIA IS WINNING THE WAR'

Russian troops have been gaining ground in the east for months, throwing huge resources into an unrelenting offensive.

Zelenskiy, speaking to Reuters in an interview this month, unfurled a once-classified map on a table in his office showing numerous mineral deposits, including a broad strip of land in the east marked as containing rare earths. Around half of it looked to be on Russia's side of the current frontlines.

The Ukrainian leader, who turned down a first draft of a minerals deal with Trump saying it did not include sufficient security guarantees, has said he wants to discuss the fate of resources on Russian-controlled territory with Trump.

He said Russia knew in detail where Ukraine's critical resources were from Soviet-era geological surveys that had been taken back to Moscow when Kyiv gained independence in 1991.

There are few reliable independent estimates of what proportion of Ukraine's natural resources Moscow currently commands. What is undisputed is that Ukraine is gradually losing control of its mineral wealth.

Vasily Koltashov, an economist and political analyst, said that Trump's desire for a grand minerals deal would prove academic if Ukraine lost the war.

"It's not him and his appetite for rare earth metals that will decide who gets what," he told Russian state TV this month. "Russia is winning in the theatre of war."

For many Russians, capturing Ukrainian natural resources also represents a major prize in the conflict, which marks its third anniversary this month.

Denis Pushilin, the top Russian-backed official in Donetsk, triggered a flurry of triumphant headlines in the Russian press last month when he incorrectly claimed that the Shevchenko deposit had been captured, confusing it with the seizure of another settlement of the same name elsewhere.

"The biggest lithium deposit in Ukraine has come under the control of Russian forces," said the government newspaper Rossiyskaya Gazeta, for example.

'MINERALS BELONG TO RUSSIANS'

The Kremlin's public reaction has so far been muted to Trump's attempt to lock Ukraine into a deal that would give the U.S. access to Ukraine's resources and provide $500 billion for U.S. aid that has already been given.

With a Putin-Trump summit on the horizon, and U.S.-Russia talks on resetting ties and considering how to end the war underway, Putin's spokesman Dmitry Peskov has said only that the American president's proposal shows he wants Ukraine to pay for any future U.S. help rather than continue to get it for free.

Maria Zakharova, a spokeswoman for Russia's foreign ministry, has spoken more bluntly, accusing Zelenskiy of offering Washington resources which he no longer controls given shifting frontlines. She also drew parallels between Trump's desire for Ukraine's mineral wealth and how the occupying Nazis stripped the country during World War Two.

"During the Second World War, the territory of the former Soviet Ukraine was seized, and the Nazis set about plundering the republic's national economy," she told a news briefing this month. "They stole cattle from the territory of Ukraine and carted black earth away. Now all this is happening non-violently, because the Kyiv regime is giving it all away."

Kyiv and Washington have both rejected accusations that the United States is unfairly seeking to exploit Ukraine's resource wealth, saying a deal over resources is in their mutual commercial and security interests.

Russian war bloggers and nationalists have made it clear they dislike what they cast as Trump's resource grab.

"There is only one thing that can be said about this," blogger Starshe Eddy told his roughly 600,000 followers on Telegram. "Don't open your gob for someone else's food. The minerals of Ukraine belong to the Russian people and nobody else."

(Reporting by Andrew Osborn; Editing by Pravin Char)