A German national competition regulatory agency waved through UniCredit's plans for a major stake in Commerzbank on Monday, removing a further obstacle to the Italian lender's ambition to take over its German competitor.

The move by the Federal Cartel Office was expected and follows a similar stamp of approval from the European Central Bank (ECB) earlier this year.

Monday's ruling allows UniCredit to own a stake of just under 30% of Commerzbank shares, compared with UniCredit's current holding of around 9.5%.

UniCredit disclosed last year that it had built a web of financial transactions through derivatives to secure a Commerzbank stake of around 28%, pending the regulatory approval, and that it ultimately desired a 29.9% stake.

"UniCredit may acquire 29.99% of Commerzbank," the cartel office said.

Commerzbank, which has been working to maintain its independence, said that the approval does not change the fundamental situation.

"UniCredit continues to be a shareholder of Commerzbank," Commerzbank said.

The question now is if and when UniCredit will act to convert the derivatives into additional shares that would put it on the cusp of a full-blown takeover of one of the most important lenders to Germany's small and medium-sized companies.

Commerzbank's largest shareholder is the German government, with a stake of around 12%.