The German government is confident the Constitutional Court will confirm an earlier ruling okaying the euro zone rescue mechanism after a June hearing to consider the bailouts and the European Central Bank's action, the finance ministry said on Friday.

"The government ... is confident the Constitutional Court will completely confirm its decision from September 12, 2012, which was made on the basis of an extensive oral hearing and on the basis of which Germany was able to legally agree to the ESM (European Stability Mechanism)," a spokesman said.

He did not go into detail about how the court might view the ECB's bond-buying plans, which it will also consider in the public hearing on June 11-12 before giving its final verdict.

In a 29-page report prepared for the court, and published in a German newspaper, the Bundesbank warns the ECB's purchase of the debt of struggling euro zone states could "compromise the independence of the central bank" and be difficult to stop.

(Reporting by Annika Breidthardt and Stephen Brown)