Updated

The European Union is concerned that Russia might want to enforce its old gas contract with Ukraine once their current arrangement runs out, saying it could contravene Moscow's peace obligations.

EU energy chief Maros Sefcovic said Thursday that any return to the previous contract between Russia's Gazprom and Ukraine's Naftogaz "would be quite difficult, complicated."

Russia and Ukraine agreed a truce this week in their latest natural gas price dispute that will ensure supplies until the end of March.

Sefcovic warned that Russian insistence on using the old contract "might really hamper the cooperation and the spirit in which also the Minsk declaration was adopted."

The Minsk agreements are responsible for the cease-fire between Ukraine and Russian-backed separatists in eastern Ukraine. The conflict has killed more than 6,000 people.