Russia's aluminum giant Rusal said on Tuesday that its board chairman Viktor Vekselberg had resigned amid a bitter struggle between its oligarch shareholders over ways to get the firm out of debt.
Vekselberg said Rusal was facing "a deep crisis" in which its problems with debt -- estimated at $11 billion at the end of last year -- were being compounded by flaring boardroom disputes over daily operations and strategy.
"UC Rusal has, in my opinion, deteriorated from an international aluminum leader into a company overburdened with debt and entangled in numerous lawsuits and social conflicts," Vekselberg said in a statement released by his Renova Group.
Rusal is operated by its biggest shareholder and Russia's one-time richest man Oleg Deripaska. The chief executive owns a 47.4-percent stake in the company through a subsidiary of his Basic Element holding.
Fellow tycoon Mikhail Prokhorov controls a 17.0-percent stake while the Russian arm the Swiss-based Glencore miner owns 8.75 percent.
Vekselberg himself controls 15.8 percent of the firm and initial rumours of his resignation had triggered a suspension of trading in the Hong Kong-listed company.
Shares in the firm, the world's biggest producer of aluminum, had already fallen 1.3 percent early on Tuesday on concern that the Russian billionaire was about to dump his Rusal stake.
Deripaska hit back at Vekselberg on Tuesday in a Rusal statement that described him as an inattentive chairman who skipped regular meetings and was about to be squeezed out by the board.
The "decision of Mr. Vekselberg to resign... pre-empted the anticipated consideration of this matter by the board," Rusal said.
Rusal was left with massive debts by the 2008-2009 financial crisis and has been under unceasing pressure from its shareholders to part with its 25-percent stake in the world's largest nickel producer Norilsk.
Vekselberg has previously sought to orchestrate the buyout with a partner while Deripaska has firmly refused to part with the stake.
Rusal managed to restructure its debt by the end of last year but has since anger shareholders by failing to follow through on its promise to begin regular dividend payments.
Its various tribulations have seen the company's shares fall more than 40 percent since its January 2010 listing.