German Chancellor Angela Merkel says she is "cautiously optimistic" that talks to resolve differences between Russia and Ukraine about the supply of natural gas will succeed.

Merkel says the dispute with Russia over its support for separatists in eastern Ukraine will likely last for some time. But she told reporters in Berlin on Thursday that she hoped European Union-brokered negotiations to secure Ukrainian and European gas supplies through the harsh winter months would bear fruit.

EU Energy Commissioner Guenther Oettinger has been brokering talks that hinge on Russia's demand for Ukraine to repay its vast gas debts.

Talking about the broader situation in Ukraine, Merkel said a U.N. report released Wednesday showing more than 300 deaths since the start of the cease-fire showed "how fragile the situation is."