MOSCOW (Reuters) - The Kremlin said on Monday that some Americans companies had shown interest in joint rare earth metals projects in Russia, but cautioned that such discussions were still at an early stage.

Striking a potential agreement on minerals extraction with Kyiv has emerged as an important element in U.S. President Donald Trump's efforts to end the war in Ukraine, and Moscow had made it clear it is also open to deals.

Russian President Putin suggested in February that the U.S. might be interested in 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 hardware.

Kremlin spokesman Dmitry Peskov said that Moscow had not signed any documents with American companies yet due to sanctions-related restrictions on U.S. firms in Russia, but he said "some of them are showing interest."

"There are no specifics here yet, but the interest is evident. The interest is mutual, because we're talking about mutually-beneficial projects", Peskov told reporters.

Putin's investment envoy, Kirill Dmitriev, told the Izvestia newspaper in comments published on Monday that talks with American firms had already begun. He did not name any companies or provide further details.

Rare earths are a group of 17 metals used to make magnets that turn power into motion for electric vehicles, cell phones, missile systems and other electronics. There are no known substitutes.

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.

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.