TOKYO, Jan 30 (Reuters) - Japanese e-commerce conglomerate Rakuten Group has raised the size of a planned dollar-denominated 3-year senior note issuance to $1.75 billion from $1 billion, according to a source close to the deal.

Rakuten announced the fundraising on Friday and said it intended to use the proceeds to pay off $1 billion worth of senior notes due in 2024.

Including the notes due in 2024, the group has a total of 800 billion yen ($5.4 billion) in debt redemptions due by the end of 2025. The debt was amassed as the cost of building out Japan's fourth mobile network carrier spiralled.

In addition to refinancing its debt, Rakuten has also listed its banking unit, sold off assets and issued new shares to shore up its finances.

The new issue will have an interest rate of around 12.25% and terms are set to be finalised in the morning of Jan. 30, U.S. Eastern time, according to the source, who was not authorised to speak publicly on the matter.

Representatives for Rakuten said they had nothing to add to the Jan. 25 statement.

News of the increase to the issue was first reported by Bloomberg.

($1 = 147.2700 yen) (Reporting by Miho Uranaka; Writing by Anton Bridge; Editing by Tom Hogue and Edwina Gibbs)