KIEV, August 20 (RIA Novosti) - Ukraine's Naftogaz and Russia's Gazprom are holding talks on a possible decrease in the volume of Russian gas to be purchased by Kiev in 2010, Ukrainian Prime Minister Yulia Tymoshenko said on Thursday.

Tymoshenko said earlier in the day that Ukraine plans to buy twice as less gas in 2010, 25 billion cubic meters, than was stipulated in the 2009-2019 contract signed by the two state-owned gas giants in January of this year.

"When the first signs of agreement between Naftogaz and Gazprom appear, I will join in for the final signing of the documents," UNIAN quoted Tymoshenko as saying.

Russia, which supplies around one quarter of Europe's gas, briefly shut down supplies via Ukraine's pipeline system at the start of the year during a dispute over Kiev's debt.

The conflict was resolved in January, when Russian Prime Minister Vladimir Putin and his Ukrainian counterpart Tymoshenko agreed deals on deliveries to and gas transit through Ukraine for 2009.

The ex-Soviet state transits around 80% of Russia's Europe-bound gas.