Eurozone states need to give up more sovereignty in order to fix the construction flaws of the euro, with the bailout fund possibly turning into a budget authority further down the road, European Central Bank board member Joerg Asmussen has said.

"We have construction mistakes of Economic and Monetary Union and it is time to correct them. It is clear that the core of the current debate has a name: further sharing of sovereignty," Asmussen said Tuesday (17 July) at the European Policy Centre, a Brussels-based think tank.

Part of the vision - which the ECB is shaping in a report drafted by EU council chief Herman Van Rompuy - is a cap on how much debt countries can issue, intervention in national budgets and fiscal corrections imposed if a country deviates from the deficit and debt limits imposed in the eurozone.

A common budgetary authority could also be formed, Asmussen said, with the upcoming permanent bailout fund, the European Stability Mechanism, a "starting point."

"The ESM is a fiscal authority by definition because it deals with taxpayers' money," he explained, adding that it would have to be put under the scrutiny of the European Parliament - or a subdivision of it pooling MEPs from eurozone countries only.

The €500bn-strong ESM is yet to be set up, pending a ruling of the Constitutional Court in Germany due on 12 September. Under current rules, the Parliament has no say over the ESM.

Asmussen said this needed to change and that the ECB itself should be under more scrutiny from the European Parliament, as it will acquire new supervisory powers of banks in the euro area.

"Deeper euro area integration can only be sustainable if there is progress on democratic legitimacy. And it should not be only the ECB continuously emphasising it," he said, adding that already now national parliaments could be involved more so that they "internalise" what it means to be an economic union.

As for the ten EU countries outside the euro area, Asmussen said they should not "fear" a multi-speed union, which is already happening. As long as the euro is not a "closed shop", but open to further members who meet the criteria, this should not be a problem, he said.

Asked if he thought all current euro members were "willing and able" to go this on this path of further sovereignty concessions, he said it was "worth fighting for" and that majorities in these countries needed to be convinced it's the only way to achieve prosperity.

The former German finance ministry official also defended the sometimes criticised stance of the ECB when giving advice to politicians on how to change the structure of the eurozone.

"It is clearly not beyond our mandate. If we can't answer where we want to be ten years from now, no one will buy a 10-year bond from us, and that is very much an issue for the ECB," he said