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

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

Putin suggested in February that the US might be interested in exploring joint exploration for rare earth metals deposits in Russia, which has the world's fifth-largest reserves of such 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 Dmitriev, who is also the CEO of the Russian Direct Investment Fund.

Trump said on Sunday he was "pissed off" at Putin and will impose secondary tariffs of 25-50 percent 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 criticized the credibility of Zelensky'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."

On Sunday, Trump repeated his suggestion that he might seek a third term as president.

In a phone call with NBC News, Trump said "I'm not joking" when asked to clarify a remark on seeking another term, adding: "There are methods (by) which you could do it."

Agencies via Xinhua