WASHINGTON (Reuters) - European Union governments should refrain from interfering with banking consolidation, which the bloc needs to compete with other major economies, two senior bank executives said on Friday.

The challenge of closer financial integration has taken fresh relevance in the euro zone after Italy's UniCredit last month unveiled a stake in Commerzbank and said it would consider a full takeover, sparking a backlash in Germany. 

UniCredit's move and Germany's defence of its second biggest bank coincided broadly with the release of a report by former European Central Bank President Mario Draghi on the EU economy. Draghi warned the EU risked "a slow agony" if it failed to embrace changes. 

"The idea that you can have 27 financial markets in Europe is simply ... crazy," Societe Generale Chairman Lorenzo Bini Smaghi told a session of the annual membership meeting of the Institute of International Finance. "But you need a shock. ... to have (a) banking union. It's a bit of a pity that Europe moves after shocks," he added.

Asked about the hurdles of a potential UniCredit-Commerzbank tie-up, ABN Amro CEO Robert Swaak said it was "very clear that ... local governments are now ... having an opinion that potentially sits at odds with what everyone else seems to be thinking, including these very governments, that there needs to be a level of consolidation".

Scope for consolidation in European banking is emerging as governments sell down stakes they acquired rescuing lenders after the 2008-2009 global financial crisis.

UniCredit bought part of its Commerzbank stake from the German government. The Dutch government last week said it would cut its stake in ABN Amro.

Bini Smaghi said shareholders alone should decide on mergers based on the value they can add.

"In the German case, it should be decided by the shareholders. Why should politicians interfere in a market they don't control in the end?".