Slovakia and Ukraine could sign a deal on European gas supplies to Kiev on Monday, they said after talks with the EU in Bratislava.
"Ukraine wants to get reverse gas flow as soon as possible but it needs more gas than it can get under the framework offered by Slovakia to secure its energy security," Ukrainian Energy Minister Yuri Prodan told reporters on Thursday.
He did not specify how much gas Ukraine would need beyond the maximum 10 billion cubic metres a year that Slovakia has proposed.
"I believe we can ink the deal on Monday in Bratislava if we can work out the remaining issues by then."
The talks were also attended by EU Energy Commissioner Guenther Oettinger and Slovak Economy Minister Tomas Malatinsky, who told reporters he hoped the deal would be signed Monday "after small changes are made".
Slovakia, as an EU member and neighbour to Ukraine, is strategically located to facilitate the pumping of gas to Ukraine from western Europe.
Such a "reverse flow" arrangement would help Ukraine reduce its reliance on Russian supplies at a time when Moscow is threatening to cut off supplies to Kiev.
Ukraine has already struck similar deals with Hungary and Poland.
Slovakia has offered the use of its smaller capacity Vojany pipeline, through which European companies could begin pumping gas to Ukraine as soon as this year.
The maximum capacity of 10 billion cubic metres a year could be reached early next year.
Malatinsky said a contract with Russian energy giant Gazprom prevents Slovakia from offering the use of a larger pipeline.
"Reverse flow through the main pipeline, currently being used for gas shipments from Russia to Europe via Ukraine and Slovakia, is legally impossible at the moment," he said.
Oettinger backed that view, saying "the solution involving the Vojany pipeline is the only legally and technically feasible solution reachable in 2014".