Kiev/Moscow - A last-ditch effort by Ukraine to pay part of a massive debt to Russia may be insufficient to prevent a natural gas supply crisis affecting Europe, according to a Thursday announcement by the Russian energy giant Gazprom.

Ukraine's government late Monday evening transferred 800 million dollars to the Russian natural gas monopolist on Tuesday, but the payment does not cover all of Kiev's outstanding debt, the Interfax news agency reported, citing a Gazprom company statement.

Ukraine owes Gazprom between 1 and 2 billion dollars for gas supplies delivered, the difference depending on whether the Ukrainian or Russian government is doing the accounting.

Ukrainian President Viktor Yushchenko on Tuesday told reporters the 800 million dollar payment would be augmented by 200 million more dollars "in the next few days ... which when paid will fully resolve Ukraine's debt," according to a Channel 5 television news report.

Gazprom spokesman Sergei Kupryanov told a press conference in Moscow that Ukraine could only pay 800 million dollars and that Gazprom had been informed that "there will be no more payments for gas supplies until the end of the year."

A contract between Russia and Ukraine on natural gas pricing is set to expire at the end of December. Russia will not renew the contract until Ukraine pays its debt in full, and is prepared to cut Ukraine off the moment the present delivery contract expires, Kremlin officials have said.

Gazprom will later on Thursday issue a "warning" to European customers of possible supply interruptions in coming days, Interfax reported.

Russian sells Europe roughly one-third of its natural gas, almost all of it delivered via pipelines crossing Ukraine. The trade is Russia's single largest export earner.

Russia in a similar pricing dispute with Ukraine cut off gas supplies to Ukraine in early 2006, in an attempt to bring Kiev to the negotiating table. The Ukrainians in retaliation siphoned Gazprom gas destined for Europe, causing price spikes as far away as Spain.

Yushchenko said Ukraine was prepared for a similar face-off at the end of 2008, saying "we have laid in reserves (of natural gas) and are ready." He made no comment on whether Ukraine intended to siphon gas destined for Europe, but added "of course we must pay our bills."

The Kremlin for years has argued Ukraine should pay international market rates for natural gas. Ukraine should pay a discounted rate as Russia has no practical way to sell gas to Europe, except via Ukrainian pipelines, Kiev has countered. (dpa)