Fortum last month closed a 3.8 billion euro ($4.4 billion)deal to buy about 47 percent in Uniper, which was opposed to the transaction from the start.

"It is fair to say that the process leading up to this day has not been without challenges. Now is the time to reset our relationship with Uniper," CEO Pekka Lundmark said in Fortum's quarterly report.

"As an initial concrete measure, we have nominated Markus Rauramo, the CFO of Fortum, to join the Supervisory Board of Uniper."

($1 = 0.8593 euros)

(Reporting by Jussi Rosendahl; editing by Jason Neely)