Ukrainian Energy Minister Yuri Prodan said on Wednesday reverse gas flows from the European Union to Ukraine had fallen because of opposition from Russian gas producer Gazprom.
Ukraine - which consumes around 50 billion cubic metres of gas annually - has increased its efforts to secure more gas from the European Union after Gazprom raised prices for its supplies in a dispute.
"Reverse gas supplies are reduced at present. This is linked to certain actions by Gazprom," Prodan told reporters, adding Ukraine first saw a decrease two weeks ago.
Gazprom declined to comment on Wednesday. The company said on Apr.5 the possibility of importing gas from the West to substitute for Russian supplies raised questions about the legality of such a move.
Gazprom head Alexei Miller has also called the reverse of gas flows from Slovakia to Ukraine "semi-fraudulent".
"You heard the threats Gazprom made to European energy companies that this reverse is illegal."
He said reverse supplies stood at 7 million cubic metres daily on Wednesday versus a possible 18 million. He did not say by how much supplies had fallen in the past two weeks.
On April 28 Bratislava and Ukraine signed a deal allowing the EU to send a limited amount of gas to Ukraine. Slovak Prime Minister Robert Fico said combined reverse flows from Slovakia, Hungary and Poland could reach up to around 16-17 bcm annually.
Reporting by Pavel Polityuk and Vladimir Soldatkin