Gazprombank, as a bank of high importance for the domestic banking sector, needs to meet higher capital requirements set out by the central bank under Basel III rules, part of a move to strengthen the banking system.

The sources did not provide a reason why Gazprom, which holds a 46 percent stake in the bank, would inject additional funds to Gazprombank, or whether the funds will be mainly used for the Basel III requirements.

"This year the bank expects to receive 10 billion roubles of additional capital in the form of perpetual subordinated deposits," a spokesman for Gazprombank told Reuters.

"Decisions to further increase will be taken by the shareholders additionally next year."

Gazprom did not reply to a Reuters request for a comment. Earlier this year the gas company provided the bank 15.5 billion roubles ($233.5 million) via a subordinated loan.