Russia's United Company RUSAL Plc <0486.HK>, the world's largest aluminum maker, descended into boardroom turmoil on Tuesday after its chairman resigned, making allegations of a debt crisis and prompting an indefinite suspension of the company's shares.

In a statement accompanying the suspension of its Hong Kong-listed stock, Rusal said its board would meet on Friday to discuss the resignation of Chairman Viktor Vekselberg and to appoint an independent director to replace him.

Earlier, media reports said Russian billionaire Vekselberg had quit because he felt Rusal faced a deep crisis and was overburdened by debt, lawsuits and social conflicts. [ID:nL2E8ED00V] Rusal, however, said he had failed as chairman.

Vekselberg had failed to perform his functions as a public company board chairman over the past 12 months, it said.

Shares in the company fell 1.3 percent to HK$6.12 on Tuesday morning before being suspended, lagging a 0.8 percent gain in the benchmark Hong Kong index <.HSI>.

Rusal, due to report its latest earnings report on March 19, posted a net profit of $432 million for the three months ended September, beating an average forecast of $409 million from 10 analysts polled by Reuters, on lower costs.

Analysts have flagged concerns over Rusal's debt burden.

We think that with concerns over its ability to service its debt load and meet its debt covenants given the currently weak aluminum prices, its shares will continue to face pressure in the near term, BOC International said in a research note in January.

Rusal could fail to meet debt covenants in 2012 if the current aluminum price weakness persists. We estimate that for Rusal to avoid breaking debt covenants, the aluminum spot needs to stay above US$2,400/t in 2012.

Aluminum prices now stand at around US$2,229.

Rusal completed its US$9.33 billion debt refinancing in September 2011 with Russian and international banks. It is no longer bound by an international override agreement (IOA) signed with lenders before its IPO, allowing it to make acquisitions and pay dividends, BOC International said.

Rusal said that at the end of September its net debt stood at US$10.91 billion.

For company statement, please read

(Writing by Anne Marie Roantree)