MILAN (Reuters) -Italy's second biggest bank UniCredit owns an equity stake of around 20%, with corresponding voting rights, in Commerzbank after converting into shares derivatives which gives it an overall 29% holding in its German rival.

UniCredit first emerged as the biggest private investor in Commerzbank in September, meeting stark opposition from Germany to full takeover plans.

Defying Berlin, UniCredit increased its position in December by buying derivative contracts. It secured European Central Bank clearance earlier this year to get to a 29.9% holding.

The Milanese bank said it had converted into shares an around 10% Commerzbank stake which it had until now held in derivatives, getting to a roughly 20% voting stake.

"UniCredit plans to convert into shares its remaining synthetic position of around 9% in due time, getting to an around 29% voting stake in Commerzbank," it said.

The moves comes after Chief Executive Andrea Orcel wrote to the new German government calling for talks over what UniCredit should do with the Commerzbank investment.

Orcel has advocated a merger of Commerzbank and UniCredit's German unit HVB as the best outcome for all stakeholders, provided a deal has broad support from all relevant parties.

He has repeatedly said he could alternatively keep the Commerzbank stake as a financial investment, or sell it. 

In his most recent letter to the new German government, Orcel has said he wants to sit down with German authorities to find the best solution for all parties involved given UniCredit's Commerzbank investment, were Berlin to continue opposing a merger.

"UniCredit is Commerzbank's leading investor," it said in the statement on Tuesday.