FRANKFURT, Oct. 16 -- The European Central Bank has cleared a major regulatory hurdle between UniCredit and control of Commerzbank, leaving a German lender that resisted the Italian bank for almost two years to deal with the shareholder it tried to keep out.

UniCredit said on Thursday that the ECB had authorised it to cross 30 percent of Commerzbank and to keep adding shares with no upper limit. The news lands hardest in Berlin, where the Merz coalition, whose finance minister, Lars Klingbeil, has pressed UniCredit for guarantees, has watched its leverage thin as the Italian bank's stake closed in on half the company.

The numbers have rough edges. Euronews reported in August that UniCredit held 47.59 percent of Commerzbank's shares, equ...