OAO Gazprom (GAZP)’s energy company and Russian billionaire Viktor Vekselberg’s Integrated Energy Systems are having difficult agreeing to merger terms because of the debts found at Vekselberg’s company, Vedomosti said, citing a source familiar with the deal.

IES’s debts were estimated at $4.4bn at the end of 2011.

Vekselberg told Bloomberg he’ll walk away from a plan to merge his power generating assets with OAO Gazprom’s if a deal isn’t completed this quarter.

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