Analysts have welcomed the move by UniCredit, particularly because a tie-up between the two banks might spur more M&A activity in Europe's banking sector.

UniCredit was able to buy 4.5% of Commerzbank from the German state because the government trusts the Italian bank, its CEO said in a newspaper interview, ruling out any "aggressive" moves such as an unsolicited buyout bid.

UniCredit SpA has demonstrated at its existing German unit that it can cut costs in the country, which bodes well for its potential plans for Commerzbank AG, analysts at KBW wrote in a note.

Opposition within the German government to a potential takeover of Commerzbank by UniCredit is solidifying, amid anger at the way the Italian bank acquired its 9 per cent stake and concern over potential macroeconomic risks a merger might pose to the German economy.

Commerzbank AG Chief Executive Officer Manfred Knof said he’ll study any proposals coming from UniCredit AG after the Italian lender bought a stake and said it wants to play an active role in the German rival’s strategy.

UniCredit's investment in German rival Commerzbank is consistent with an "excellent" geographic diversification strategy, the chief executive of Italy's top lender Intesa Sanpaolo said on Wednesday, adding that his bank had a different approach.