In a televised statement, Alexei Miller, Gazprom chief executive, said: "The countdown has started. If Ukraine doesn't pay off the debt by December 31, Gazprom will have no grounds to continue shipping gas to Ukraine."

Miller said Ukraine would also face sharply higher payments for future deliveries if it did not act.

Ukraine had faced a replay of a similar crisis in January 2006 when a cut off of Russian gas shipments resulted in a brief reduction of supplies in Europe.

Gazprom supplies a quarter of the gas used by European Union nations, with around 80 per cent of it passing through Ukraine.

The global financial crisis has hit Ukraine harder than most other European countries, and Kiev was recently forced to seek $14.5bn in aid from the International Monetary Fund.

On Monday, Vladimir Putin, Russia's prime minister, said he had spoken on the telephone to Viktor Yushchenko, Ukraine's president for "almost an hour".

"They don't want to pay," said Putin.

Profit rise

Meanwhile, Gazprom revealed a significant rise in profits following record gas and oil prices in the first half of 2008.

Net profit rose 85% to $20.8bn compared with the same period last year.

However, Gazprom said that the recent fall in oil prices and the global credit crunch would affected future profits.

In a statement on Tuesday, the company said: "At the moment the management can not certainly assess the impact of further decrease in financial markets' liquidity and the growing instability of foreign exchange and stock markets on the group's financial state."