EU Energy Chief: 'We Need a United States of Europe'

European Union Energy Commissioner Gunther Oettinger said "we need a United States of Europe" and that "there is no 'Plan B'" for the euro zone, in an interview with CNBC on Wednesday.

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Speaking at the sidelines of the 161st ordinary meeting of the Organization of Petroleum Exporting Countries in Vienna, Oettinger emphasized the need for European leaders to act quickly to stem the continent's worsening debt crisis. "We have to bring some concrete proposals" to the summit of European leaders to be held on June 28-29, he said.

Europe, he said, needs "a common political approach," and needs to "harmonize taxation" and "coordinate economic policies." He added that all European institutions "know our obligation" on that front, and that "we have to be a common European team."

Oettinger defended German Chancellor Angela Merkel's handling of the crisis and said he expects her and French President Francois Hollande to work more closely together after the French parliamentary elections take place this weekend.

Oettinger said Europe's main tools to solve its crisis are the temporary Emergency Financial Stability Fund, or EFSF , and its permanent successor, the European Stability Mechanism, the latter of which he said would provide up to 500 billion euros of firepower for struggling European governments once it is up and running July 1.

He said the EFSF, meanwhile, "will work one year longer than planned." Common euro bonds, however, should come "afterwards," he said, reiterating the German stance that such bonds would remove the incentive for nations to make needed structural reforms.

As for whether Greece stays in the euro zone, Mr. Oettinger said he would prefer that to happen but that the decision was ultimately up to Greek voters. But he reiterated that "there is no Plan B" for the monetary union.

—By CNBC's Kelly Evans