OSLO, June 21 (Reuters) - Lufthansa said on Wednesday it has agreed to sell its AirPlus payments subsidiary to Swedish bank SEB for around 450 million euros ($491 million), boosting the German airline group's operating margin and return on capital.

"As part of a larger financial group, (AirPlus) will be able to realise its potential better than in the Lufthansa Group," Chief Financial Officer Remco Steenbergen said in a statement.

"In turn, it enables us to focus even more on further improving the profitability and capital return of the Lufthansa Group core business," he added.

SEB in the joint statement said the merger of its Kort unit with AirPlus will make the bank "a European leader in corporate payment solutions" and boost SEB's broader corporate banking ambitions in Germany, Austria, Switzerland and northern Europe.

The transaction includes all international subsidiaries and branches of AirPlus, the companies said.

($1 = 0.9163 euros) (Reporting by Terje Solsvik in Oslo and Tristan Chabba in Gdansk; Editing by Tom Hogue and Sherry Jacob-Phillips)