The European Union shares Ukraine's alarm on the loss of Crimea and billions of losses from this and agrees with its legal claims, European Energy Commissioner Gunther Oettinger has said.

"We believe that the accession of Crimea to Russia is not in line with international law. It is unacceptable. At present, the talks [on the price of gas] continue," he said at a press conference in Brussels during the presentation of a new European Energy Security Strategy.

He warned that the inclusion of the Crimean issue in the gas talks might deadlock them.

Oettinger said the EU is calling on Ukraine to separate the gas issue from the Crimean issue and not try to resolve it within the next few days or weeks.

He said that the EU agreed with Ukraine that there are other legal issues and there is a possibility of settling them via the Stockholm Arbitration Institute, but it may take many months to deal with.

The road to Stockholm is open for Ukraine, but other issues should be settled, he said.

Oettinger said that the talks should be held to achieve the price of gas, a fair price. The issue should be settled in coming days.

"No one excludes other important issues from the talks, but we believe that they cannot be settled in the short term," he said.