Live updates: follow the latest news on Russia-Ukraine
A veteran aide to Russia's President Vladimir Putin has resigned, becoming the most senior figure to break with the Kremlin since Mr Putin launched an attack on Ukraine one month ago.
Anatoly Chubais, the president's special envoy to international organisations, was an architect of Russia's post-Soviet economic reforms in the 1990s and was Mr Putin's superior when the future president first joined the Kremlin. He later ran big state businesses under Mr Putin and held a number of political jobs.
Kremlin spokesman Dmitry Peskov told the Ria Novosti news agency on Wednesday Mr Chubais had resigned of his own accord. He gave no further details.
Mr Chubais has left Russia, according to sources who spoke to Reuters. The agency said he hung up when contacted by phone.
His resignation comes as Russia faces international isolation over Mr Putin's decision to invade Ukraine on February 24. Western sanctions have sought to cut Russia off from the global economy and targeted senior Russian figures including Mr Putin, as well as oligarchs linked to the president.
The war has driven a quarter of Ukraine's 44 million people from their homes and killed thousands of civilians and combatants. Russian forces are attacking the capital, Kyiv, but have so far failed to capture a single major city. Moscow says its aim is to disarm its neighbour, and its "special military operation" is going to plan. It denies targeting civilians.
Western leaders are expected to roll out additional sanctions, including possible measures targeting Russian members of parliament, after an emergency summit of Nato and European leaders at the military alliance's headquarters in Brussels on Thursday.
A western official said the resignation of Mr Chubais, who once served as former president Boris Yeltsin's chief of staff, was a "significant statement" but unlikely to have wider repercussions for Russia's leadership.
Mr Chubais was "relatively high up on the list" of people who might take such a step, the official told Reuters.
"I think it's encouraging that there are senior members of the Russian political class that are doing such things, but it doesn't lead me to a conclusion that this is in any way undermining the security of Putin and his regime, given the iron grip that he holds together with those at the centre of his power," the official said.
"But nonetheless, I think it is an encouraging statement that such a figure would make this move."
Russia has taken strong steps to contain domestic criticism of the war in Ukraine, including the arrests of thousands of protesters and a new law against discrediting the armed forces.