Gazprom is saying that Ukraine will this winter experience a roughly 30% shortage of gas reserves in underground storage for ensuring the transit of Russian gas to Europe, which will create a catastrophic situation.

"The Ukrainian colleagues, finding themselves in a difficult economic situation paying gas debts, have completely stopped buying Russian gas and begun taking gas out of underground storage in western Ukraine," deputy Gazprom chief Vitaly Markelov told the press.

"Ukraine's system of trunk pipelines was set up in the Soviet era as part of the unified gas-supply system. Gas moves to Europe through Ukraine in the east and for Ukrainian consumers transit gas is taken, I emphasize, transit gas with replenishment from underground storage facilities that are located in the west of Ukraine," he said.

"The Ukrainian colleagues pumped into underground storage this year all of only 17.6 billion cubic meters, which is very little. And there are great risks to [them] getting through the fall-winter period. For uninterrupted gas transit 21.5 billion cubic meters had to be pumped. But now the Ukrainian colleagues have begun taking gas out of underground storage, when the winter period has not yet begun. At such outtake rates, Ukraine may have around 14 billion cubic meters left in underground storage when it starts getting cold. That is a catastrophe. In such conditions, the transit of gas from Russia in winter conditions is impossible for the reason that the gas in underground storage will not suffice to compensate for outtake by Ukrainian consumers," Markelov said.

"We are getting a squall of calls. Consumers in Europe are worried about the situation that has developed. Everyone understands the risks. The situation is serious. We are prepared to look for compromises and are hoping we will find a solution," he said.

Gazprom is examining the possibility of giving Naftogaz Ukrainy new payment extensions for gas deliveries, the head of the Russian gas giant's foreign economic department, Pavel Oderov, said during a conference call for investors.

Ukraine has regularly requested more time to pay for gas since 2012.

"There is unpaid debt for August and October. The question of providing a payment extension is being examined," Oderov said.

Naftogaz halted gas imports from Gazprom at the beginning of November. "In fact, this means that domestic production and gas in underground storage is being used to supply the domestic market," Oderov said, adding that gas is needed in Ukraine's underground storage in order to ensure uninterrupted transit, which may be jeopardized by withdrawals for the domestic market.

Deputy CEO Andrei Kruglov said: "As financial people, we see that Ukraine's indebtedness is growing and now tops $1.3 billion. And we are not seeing any change."

Gazprom has provided a payment extension on Ukraine's debt for gas delivered in August, at 6% annual interest.