BRUSSELS (AP) — Russian and Ukrainian negotiators have failed to agree on a new long-term natural gas transit contract, raising the specter of possible supply cuts during the winter.

EU Energy Commissioner Maros Sefcovic says he is "disappointed" by the outcome of Monday's talks in Brussels and warns that "time is flying" as the current gas contract expires on Jan. 1.

Russia and Ukraine have been embroiled in numerous gas price wars and concern is mounting that Russia could turn the taps off again. A lot of Russian gas bound for Europe transits Ukraine.

Sefcovic, who supervised the talks, says all sides "agree that the disruption of supplies is absolutely a non-option."

He is appealing to the negotiating teams to be prepared for a new round of talks, hopefully in a few weeks.