Gazprombank has demanded early repayment of a loan of $842.5 million to Dmytro Firtash's Ostchem, the bank said in a statement.

"In connection with the inability of Ostchem Holding Ltd to uphold its commitments to Gazprombank under their agreement on a loan of $842.5 million, the bank is compelled to declare the loan and accumulated interest subject to immediate repayment," the statement says.

If the money is not repaid by December 30, 2014, - Gazprombank earlier agreed to putting back the repayment deadline to the end of 2014, - the bank would demand that the loan guarantors, four mineral fertilizer manufacturing plants belonging to the Ostchem group, hand over to it the collateral, 5.68 billion cubic meters of gas from Ukrainian underground depots, the lender says.

Reports in November 2013 said Ostchem had acquired about 5 billion cubic meters of gas from Russia under a credit deal with Gazprombank. The gas, which was to be pumped into underground depots, was priced at $268.5 per 1,000 cubic meters, which meant the loan amounted to $1.34 billion. The same month, Firtash confirmed the existence of the deal.

On the whole, Ostchem imported about 12.92 billion cubic meters of gas from Russia that year, practically as much as Ukrainian state oil and gas company Naftogaz did in 2013.

As of mid-September 2014, Ukrtransgaz held about 16.5 billion cubic meters of gas in its underground depots. This amount included 3.5 billion cubic meters that belonged to Ostchem, about 1 billion belonging to other private companies, and about 14 billion cubic meters owned by Naftogaz and its subsidiaries.

By December 13, 2014, the depots of Ukrtransgaz contained 12.65 billion cubic meters of gas.