Vekselberg's exit widens a rift with controlling shareholder Deripaska, who had sought to build a Russian metals and mining business on a global scale by merging Rusal with Norilsk Nickel, the world's top nickel and palladium miner.

"I regret to say at this time that Rusal is in a deep crisis, caused by the actions of the management," said Vekselberg. Deripaska bought a one-quarter stake in Norilsk through Rusal four years ago but the debt-financed deal quickly turned sour when the global crisis hit.

Rusal was forced into a debt restructuring, killing Deripaska's dream of a mega-merger. But he has blocked calls by his partners - Vekselberg and billionaire politician Mikhail Prokhorov - to sell the stake back to Norilsk.

Rusal accused Vekselberg of failing to fulfil the role of chairman and indicated he would have been removed in any case.

"Vekselberg had failed to perform his functions as a public company board chairman over the past 12 months," it said, adding that he had not attended a board meeting since February 2011.

"In this respect, the decision of Mr Vekselberg to resign as chairman of the board preempted the anticipated consideration of this matter by the Board."