Russian climate envoy Anatoly Chubais has stepped down and left the country, citing his opposition to President Vladimir Putin’s war in Ukraine, according to two people familiar with the situation, becoming the highest-level official to break with the Kremlin over the invasion.

Chubais, 66, is one of the few 1990s-era economic reformers who’d remained in Putin’s government and had maintained close ties with Western officials. Kremlin spokesman Dmitry Peskov didn’t immediately respond to a request for comment.

Known as the architect of Russia’s 1990s privatizations, Chubais gave Putin his first Kremlin job in the mid-1990s and initially welcomed his rise to power at the end of that decade. Under Putin, Chubais took top jobs at big state companies until the president named him envoy for sustainable development last year.

Chubais announced his resignation in a letter to colleagues and friends Tuesday, according to people who saw it. Last week, he hinted at a darkened outlook, saying in a post on Facebook on the anniversary of the death of Yegor Gaidar that the fellow economic reformer “understood the strategic risks better than I did and I was wrong.”

In his 2006 book, “Death of Empire,” Gaidar warned of the temptations of imperial nostalgia for the Soviet Union he saw growing under Putin. “It’s not difficult to convince society that a state that collapsed so suddenly can be just as quickly rebuilt,” he wrote. “That’s an illusion, a dangerous one.”

Since the war, the government has stepped up pressure on domestic critics of the invasion. Putin warned on March 16 that he would cleanse Russia of the “scum and traitors” he accuses of working covertly for the U.S. and its allies. Facing economic meltdown, the Russian leader accused the West of wanting to destroy Russia.

“Any people, and particularly the Russian people, will always be able to tell the patriots from the scum and traitors and spit them out like a midge that accidentally flew into their mouths,” Putin said. “I am convinced that this natural and necessary self-cleansing of society will only strengthen our country, our solidarity, cohesion and readiness to meet any challenge.”

Last week, Arkady Dvorkovich, who was senior economic adviser to Dmitry Medvedev during his presidency and a deputy prime minister until 2018, stepped down as head of the state-backed Skolkovo technology fund after condemning the invasion. Dvorkovich, who’s also president of the International Chess Federation, is one of only a few former senior officials to speak out against the war.