By Guy Faulconbridge and Lidia Kelly

MOSCOW (Reuters) -Russia and the United States have started talks on joint rare earth metals and other projects in Russia, and some companies have already expressed an interest in them, President Vladimir Putin's investment envoy said in remarks published on Monday.

Amid efforts by U.S. President Donald Trump to end the war in Ukraine, minerals cooperation has been floated by both Kyiv and Moscow, though Trump said on Sunday that Ukrainian President Volodymyr Zelenskiy wants to back out of a proposed deal.

Putin in February suggested that the United States might be interested in exploring joint exploration for rare earth metals deposits in Russia, which has the world's fifth-largest reserves of the metals used in lasers and military equipment.

Kirill Dmitriev, Kremlin special envoy on international economic and investment cooperation, told the Izvestia newspaper in remarks published on Monday that talks had already begun.

"Rare earth metals are an important area for cooperation, and, of course, we have begun discussions on various rare earth metals and (other) projects in Russia," said Kirill Dmitriev, who is also the CEO of the Russian Direct Investment Fund.

Dmitriev, who was part of Russia's negotiating team at talks with U.S. officials in Saudi Arabia in February, said some companies have already shown interest in the projects. He did not name any companies and did not reveal further details.

Trump said on Sunday he was "pissed off" at Putin and will impose secondary tariffs of 25% to 50% on buyers of Russian oil if he feels Moscow is blocking his efforts to end the war in Ukraine.

Trump told NBC News he was very angry after Putin last week criticised the credibility of Zelenskiy's leadership, the television network reported. Trump later reiterated to reporters he was disappointed with Putin but added: "I think we are making progress, step by step."

China's control of 95% of global production and supplies of rare earth metals, crucial for industries such as defence and consumer electronics, has focused the rest of the world on trying to develop their own supplies.

The U.S. Geological Survey estimates Russia's reserves of rare earth metals at 3.8 million metric tons but Moscow has far higher estimates.

According to the Natural Resources Ministry, Russia has reserves of 15 rare earth metals totalling 28.7 million tons as of January 1, 2023 and that 3.8 million tons is the amount of reserves under development or ready for development.

Izvestia reported the cooperation may be further discussed at the next round of Russia-U.S. talks that may take place in mid-April in Saudi Arabia.

(Reporting by Lidia Kelly in Melbourne and Guy Faulconbridge in Moscow; Editing by Bill Berkrot, Chris Reese and Ros Russell)