Germany on Tuesday formally rejected UniCredit's offer for Commerzbank shares, citing a low price and concerns about what it called the Italian lender's aggressive approach.

UniCredit's initial offer period for Commerzbank shares is winding down, with both banks digging ​in their heels in the months-long battle for control of one of Germany's most important lenders.

On Monday, the Italian bank hailed the fact that it had exceeded the 30% threshold it had set for this takeover bid. The Milan-based lender launched its bid, valued at 35 billion euros ($40.6 billion), in early May to gain control of its German rival and cement its status as a European heavyweight.

The ​German government holds a 12% stake in Commerzbank acquired in the wake of the ⁠2008 global financial crisis and has long objected to UniCredit's campaign for a tie-up.

"Accepting the offer was ​already not an option from a financial point of view, as it does not include an appropriate premium ​on the current share price of Commerzbank’s shares," the country's finance agency said on Tuesday.

Despite Berlin's position, UniCredit could still win control of the German bank, but the government's stake gives it seats on Commerzbank's supervisory board, which appoints management and helps oversee its strategy.

Financial Market Stabilization Fund, which manages the government's holdings, also said that it supported Commerzbank's independence, and noted that the ​bank played a critical role in financing medium-sized Mittelstand companies and was an integral player in Frankfurt, the nation's financial ‌hub.

"Both ⁠must continue to be ensured in the future," it said.

Separately, Frankfurt prosecutors on Tuesday confirmed that they had begun a preliminary investigation into "possible market manipulation" related to the offer, without providing details.

It follows a criminal complaint filed by Commerzbank's workers' council that reached prosecutors on Sunday. The employee group had communicated to staff ​that they would file ​the complaint against unspecified ⁠persons amid questions about UniCredit's acquisition of Commerzbank shares at a below-market rate.

UniCredit said in a statement that it was aware of the matter and that the ​prosecutors' response was "in line with protocol when such complaints are filed."

In Tuesday's trading, ​Commerzbank shares slipped ⁠below the price implied by UniCredit's buyout offer, after trading consistently above that level since the bid was launched and rendering Italian bank's offer relatively unattractive.

Shares in Commerzbank were trading at 36.53 euros by 0812 GMT, while those of UniCredit ⁠were at 76.97 euros. ​With an exchange ratio of 0.485 new UniCredit shares for each ​Commerzbank share tendered, the Italian bank's bid values Commerzbank at 37.33 euros a share.

The offer ends on Tuesday but will extend for a further ​15 days from June 20.

If the offer succeeds and is approved by the European Central Bank (ECB), it should mainly allow UniCredit to gradually increase its stake in Commerzbank and merge it with its German subsidiary HypoVereinsbank.

In particular, the Milan-based bank is proposing to cut back Commerzbank's international network, deemed too complex and inefficient, and refocus the bank on its activities in Germany.

Chancellor Friedrich Merz said in May the bid was destroying "trust" in Germany's second-largest private bank.

Seeking to fend off the advances, Commerzbank's CEO Bettina Orlopp unveiled a strategic plan to strengthen profitability through 2030, including job cuts to become leaner and more attractive to shareholders.

UniCredit has meanwhile asserted that by surpassing the 30% threshold of voting rights, it should be allowed to appoint all of the shareholder representatives to the supervisory board, where two representatives of the German state currently sit.

Orlopp has contested that position, pointing to an agreement with Berlin that guarantees Commerzbank the power to propose the state's representatives to the board.