Ukraine's national oil and gas company Naftogaz Ukrainy intends to return to Gazprom the additional payment for gas transit that the Russian gas giant announced it had made earlier on Thursday, Naftogaz's press service told Interfax-Ukraine.

Naftogaz Ukrainy believes the payment was made erroneously, is studying the issue and plans to return the money to Gazprom, the spokesman said.

Gazprom said that increases in the price it charged Ukraine for gas resulted in an increase in transit fees, which are tied to the gas price. As a result, the advance payment for transit of Russian gas through Ukraine made earlier ran out in July and cash payments for current gas transit commenced that month.

Ukraine in turn does not consider Gazprom's increase in gas prices to $485.5 legally valid and is therefore not raising transit rates for Gazprom.