The next round of negotiations between Russia and Ukraine over the former's gas supplies to Ukraine will not take place in Berlin next week as initially scheduled, the European Commission said Friday.

The commission said in a statement today that the meeting was postponed because too many issues remain open. German news agency DPA reported today that the EU's top energy official Maros Sefcovic, said more preparation was needed before the Russian and Ukrainian energy ministers can resume their negotiations, as had been scheduled for Tuesday.

Ukraine is heavily dependent on energy from Russia and is also a key transit country for supplies to Western Europe. The European Union has been mediating in gas disputes between the two sides, whose relations are strained by the conflict in eastern Ukraine.