Anatoly Chubais has stepped down from his role as an international envoy for President Vladimir Putin, the most senior official to resign since Russia’s invasion of Ukraine.
Russian reports said he was currently in Turkey with his wife.
Mr Chubais was given the job of coordinating Russia’s sustainable development goals internationally.
After the war began he posted a picture of a murdered opposition figure, in what was seen as a critical gesture.
There was no comment to accompany his Facebook photo of Boris Nemtsov, on the anniversary of his killing in view of the Kremlin. He has also made no comment yet on his resignation.
A source told the Tass news agency that he had left Russia as well as resigning as a special representative to President Putin.
“Yes, Chubais has resigned of his own will. But whether he has left [Russia] or stayed, that’s his personal affair,” said Kremlin spokesman Dmitry Peskov.
Other than Mr Peskov and Foreign Minister Sergei Lavrov, few members of the president’s circle have appeared in public in recent weeks.
Ukrainian presidential adviser Mykhaylo Podolyak said on Wednesday that it was interesting that the two top security figures, Defence Minister Sergei Shoigu and Chief of Staff Valery Gerasimov, were “nowhere to be seen”, along with the heads of Russia’s secret services.
Chubais was not seen as a Kremlin insider, despite having the post of special representative for ties with international organisations.
He is best known for his controversial role in helping to reform Russia’s economy in the 1990s after the fall of the Soviet Union. The raft of privatisations under President Boris Yeltsin helped create a large number of very wealthy oligarchs.
Opposition figures were unimpressed by Mr Chubais’s resignation. Jailed leader Alexei Navalny’s spokeswoman, Kira Yarmysh, cast doubt on claims that it was an anti-war protest, rather than “out of fear for his own skin and his own money”.
Russia has clamped down on criticism of the invasion, which began on 24 February, requiring state-run media to describe it as a “special military operation”.
Several state TV journalists have resigned, including Channel One editor Marina Ovsyannikova, who held up a poster saying “Stop the War!” during a prime-time news broadcast, telling Russians they were being lied to.
A new law bans the dissemination of “false news” about the war and political journalist Alexander Nevzorov became the most prominent figure yet to be prosecuted, after he posted details on social media about Russia’s deadly attack on a maternity hospital in the southern Ukrainian city of Mariupol.