Gazprom Chairman Alexei Miller met Thursday in Moscow with Andrey Kobolev, the chief executive officer at Ukrainian energy company Naftogaz.
"The focus of the meeting fell on the necessity for Naftogaz of Ukraine to take the urgent action aimed at settling the accumulated debt for the supplied Russian gas," Gazprom said in a statement.
The Russian energy company said it's owed $2.2 billion, including overdue payments for March supplies.
Gazprom in 2009 cut gas supplies to Ukraine because of disputes over debt. The Russian company said recently it would increase by $100 per 1,000 cubic meters, the standard purchase volume, the amount Ukraine pays for gas.
The International Energy Agency last month said there have been no physical disruption in supplies of natural gas running from Russia trough the Ukrainian transit system.
Gazprom, however, said it has "grave" concerns about the working gas capacity left in Ukraine's storage facilities.
"In this situation they need to be replenished right now to satisfy the domestic demand during the forthcoming winter and, accordingly, to enable Naftogaz fulfill its obligations on uninterrupted Russian gas transit to Europe," the Russian company said.