Steel company Esmark Inc said on Wednesday it has been unable to refinance its debt on a long-term basis, raising substantial doubt about its ability to continue as a going concern.

The statement was required by a Nasdaq rule, the Wheeling, West Virginia-based company said.

It was prompted by Esmark's annual report on Form 10-K, filed on May 20, which included an explanatory paragraph from the company's accounting firm.

Last week, Russian metals and mining company OAO Severstal commenced its $17 per share tender offer for outstanding common stock of Esmark.

Severstal's bid, worth about $1.24 billion, is backed by the United Steelworkers union, which had threatened to block an earlier offer to buy Esmark from India's Essar Steel Holdings.

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