(Updated - October 30, 2017 1:18 PM EDT)

Softbank is planning to call off the merger of subsidiary Sprint Corp. (NYSE: S) and T-Mobile (NASDAQ: TMUS) as the two sides have failed to agree on an adequate ownership structure of the combined entity, Nikkei reported.

Softbank is expected to approach T-Mobile owner Deutsche Telekom as early as tomorrow to propose ending the negotiations, the report added.

Deutsche Telekom has insisted on a controlling stake, according to a source cited by Nikkei, something that SoftBank's board is not willing to give up.