Billionaire investor and Norilsk Nickel board member Mikhail Prokhorov warned on Monday that a planned $2 billion share buyback could push the company to bankruptcy.

The announcement steps up a battle between billionaire Vladimir Potanin's Interros holding and United Company RusAl, in which Prokhorov has a minority stake, for control of Norilsk, and it could represent an effort by RusAl to receive a dividend.

Norilsk's board, controlled by Potanin, voted in late August to begin a buyback of around 4 percent of its shares Oct. 29 to shore up the miner's value in the melting financial markets. Norilsk's shares closed down 0.8 percent on the MICEX Index, beating the overall market.

The repurchase would tie up capital needed to upgrade plants, service more than $8 billion of debt and complete obligatory investment programs at Norilsk's electricity assets, Prokhorov said in an open letter to Potanin.

It will also take place as the metals that the company produces are falling in price, Prokhorov said, demanding that the board meet to reverse its vote.

"I believe the decision to buy back shares worth $2 billion is at this point extremely untimely and capable of driving the company to the verge of bankruptcy," he said in the letter, posted on the blog of his Onexim investment vehicle.

A spokeswoman for Interros declined to comment Monday.

Prokhorov owns 14 percent of RusAl, which is controlled by Oleg Deripaska. RusAl is the second-largest Norilsk shareholder with a 25 percent stake purchased from Prokhorov. Potanin's Interros holds around 30 percent.

Prokhorov likely wants to prevent Norilsk from spending the money so that debt-ridden RusAl can receive larger dividends this year, said Nikolai Sosnovsky, a metals analyst at UralSib.

RusAl has debts totaling $14 billion, including loans used to buy the Norilsk stake.

"RusAl shareholders are trying their best to get some dividends from Norilsk," Sosnovsky said. "It's quite an important element of the battle."

Prokhorov's concerns about Norilsk's financial footing make sense, but the company's net debt is not too large compared with its estimated earnings for this year, said Sosnovsky and Dmitry Skvortsov, a metals analyst at the Bank of Moscow.

RusAl most recently demanded an extraordinary shareholders meeting to seat more independent directors on the board, including Fiat chairman Luca Cordero di Montezemolo.

Prokhorov's letter also appeared on his personal blog Monday afternoon but was removed within two hours. He said the letter was a formal request for the board to review the matter at a meeting Oct. 20 or any other time before Oct. 29.

Prokhorov indicated that Norilsk would need to borrow some of the $2 billion on the constricted financial market to buy the stock from investors at 4.5 times its market value.

He also brought up the fact that three Norilsk subsidiaries handed about $1.8 billion for management to a bank, which decided to spend it on Norilsk shares. Norilsk announced the move late last month.

Combined, the buyback and the subsidiaries' acquisitions reflect a desire by the "majority shareholder … to improve his financial position and increase his effective control over the company's share capital," Prokhorov said.