BRUSSELS, June 9 - Trilateral talks bringing together Russia, Ukraine and the European Commission will resume on Tuesday or early on Wednesday after eight hours of negotiations failed to get a deal on Monday, Reuters reported, citing a Commission spokeswoman.

Russia has threatened to cut of gas supplies to Ukraine as early as Tuesday, with possible knock-on effects for EU supplies, because Ukraine has failed to pay its gas bill.

"The talks will continue either Tuesday evening or Wednesday morning," Commission spokeswoman Sabine Berger told Reuters after around eight hours of talks, which ended around 3 a.m. (0100 GMT).

Russian Energy Minister Alexander Novak, Ukrainian Energy Minister Yuri Prodan and the CEOs of Russian gas producer Gazprom and Ukraine's Naftogaz would took part in the Brussels talks, brokered by EU Energy Commissioner Guenther Oettinger.

After popular protests toppled a pro-Moscow Ukrainian president in February, Russia raised the price it charges Ukraine for gas and has threatened to cut off supplies on Tuesday if Kiev does not pay its overdue bills. Moscow has also annexed Crimea from Ukraine, while armed pro-Russian separatists have tried to split off some eastern parts of the country.

Monday's talks follow a tentative rapprochement last week when newly installed Ukrainian President Petro Poroshenko and Russia's Vladimir Putin met in France at commemorations of the World War Two D-Day landings.

The negotiations, which began shortly after 7 p.m. (1700 GMT) on a public holiday in much of Europe, follow four previous rounds of trilateral talks as well as bilateral conversations between the two CEOs.

Arriving for the meeting, Oettinger told reporters the CEOs had contacted him at the weekend and asked for trilateral talks to resume as soon as possible.

Separately on Monday, Ukraine said it had reached a "mutual understanding" with Moscow on parts of a plan proposed by Poroshenko for ending the conflict with the rebels in the east.

The European Union gets roughly a third of its gas imports from Russia, and almost half of that is sent via Ukraine, so if Gazprom cuts off gas to Ukraine, the EU could also face supply disruption. (rt/ez)