By Anton Bridge

TOKYO (Reuters) -Japan's Rakuten on Tuesday logged its fifteenth consecutive quarter in the red as losses at its mobile service network unit outweighed a record performance from its financial unit.

The internet conglomerate logged an operating loss of 33.3 billion yen ($213 million) in January-March, in line with estimates. The result was around half its loss in the same quarter a year earlier but little changed from the previous quarter.

Its financial unit which offers online banking, brokerage, credit card and insurance services, logged an operating profit of 39.3 billion yen, up 47% from a year earlier, as its customer base grew.

But the mobile business, which has struggled with huge build-out costs and lacklustre subscriber growth since its launch in 2020, recorded an operating loss of 71.9 billion yen.

While its number of mobile subscribers rose to 6.48 million at the end of March - increasing by around 1.5 million since the end of August last year - average revenue per user (ARPU) increased only fractionally.

Rakuten has offered generous joining bonuses for new customers, who gain further discounts and perks across the other services in Rakuten's ecosystem, helping generate subscriber growth but limiting the unit's profits.

The building out of the mobile network has resulted in massive debt and Rakuten has 627 billion yen ($4 billion) of outstanding bonds to be redeemed by the end of 2025, according to LSEG data.

Chief Financial Officer Kenji Hirose, however, told a briefing that he was confident in Rakuten's capacity to refinance its upcoming debt redemptions.

In January, Rakuten refinanced around $1.75 billion of its U.S. dollar-denominated debt at an interest rate of 11.25%, to be paid off in 2027. The new fundraising helped Rakuten redeem two tranches of bonds which had interest rates of 10.25% and 3.546% respectively.

($1 = 156.4600 yen)

(Reporting by Anton Bridge; Editing by Edwina Gibbs)