European Energy Commissioner Guenther Oettinger however said "significant progress" was made after the talks broke up between the Ukrainian and Russian energy ministers, Yuri Prodan and Alexander Novak.
"We hope for an agreement next week," he said of the new round of talks scheduled for October 29.
Russia in mid-June cut supplies to Ukraine, demanding the new pro-Western government in Kiev pay sharply higher prices in advance for new deliveries after it ran up what Moscow claims is an unpaid bill of USD 5.3 billion.
According to Oettinger and Novak, there was agreement on the price of gas, at USD 385 per 1,000 cubic metres of gas for deliveries guaranteed through the end of March.
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But the "major obstacle" to an agreement is that Ukraine has not paid its gas bills for months, Oettinger said.
Hopes for a deal improved after Ukrainian President Petro Poroshenko and Russian counterpart Vladimir Putin reached a preliminary deal at an EU summit last week in Milan.
According to Novak, Ukraine must pay USD 1.450 billion to resume deliveries, and that "it lacked USD 1.6 billion" needed to pay in advance for deliveries in November and December.
"Over the next week, the European Commission and Ukraine will look into how they can find the cash to honour the bills for November and December," Novak said, adding that so far there are no guarantees from Naftogaz or the European Commission.
The loan request "will now be evaluated in consultation with the IMF and Ukrainian authorities, and a proposal will be made," Commission spokesman Simon O'Connor said.
In Milan last week, Putin implied an accord was close but urged EU governments to help Ukraine finalise the complex funding it needs to afford the deal.
German Chancellor Angela Merkel, speaking in Bratislava yesterday, said EU member states should do their part.