Six-year-old Grab has garnered more than $6 billion in total funding, led by SoftBank, Chinese ride-hailing firm Didi Chuxing and Toyota Motor Corp. After its last funding a few months ago, Grab was valued at around $11 billion.

SoftBank first bought a stake worth $250 million in Grab in 2014 and has invested more subsequently. A doubling down on Grab with new funding would underscore SoftBank's confidence in the ride-hailing company's aggressive expansion after it acquired Uber Technologies Inc's Southeast Asian business this year.

Singapore-headquartered Grab is looking to transform itself into a leading consumer technology group, offering services such as food and parcel deliveries, electronic money transfers, micro-loans and mobile payments, besides ride-hailing, in one of the world's fastest growing markets - home to some 640 million people.

"Grab is going into so many verticals to become the dominant platform play. SoftBank clearly sees it as the long-term winner in this huge market," said one source.

SoftBank did not comment for the story when contacted by Reuters. Grab declined to comment. The sources declined to be identified as the information is not public.

The sources said SoftBank and Grab are in advanced talks to finalize terms of the latest investment and Grab's latest funding round is likely to be completed in a few weeks. It was not clear which unit of SoftBank is making the investment.

Grab is likely to tap strategic and financial firms for the remainder of the funding and this could be the final major funding before a potential IPO in a few years, the sources said.

It has already raised $2 billion this year, led by Toyota and financial firms, to fuel its expansion that has now taken its ride-hailing business to 235 cities in eight countries in Southeast Asia.

Ride hailing services in Southeast Asia are expected to surge to $20.1 billion in gross merchandise value in 2025 from an estimated $5.1 billion in 2017, according to a Google-Temasek report.

Grab's app has been downloaded more than 109 million times and it has clocked more than 2 billion rides so far.

Within Southeast Asia, Indonesia - home to 250 million-plus people - is shaping up as a battleground for global technology giants such as Alibaba, Tencent Holdings Ltd, JD.com, Google and SoftBank in the fight for market share in ride-hailing, online payments and e-commerce.

Grab has earmarked Indonesia as a priority market as competition heats up with Indonesian rival Go-Jek expanding into Southeast Asia.

(Reporting by Anshuman Daga in SINGAPORE and Cindy Silviana in JAKARTA ; Additional reporting by Sam Nussey in TOKYO; Editing by Sumeet Chatterjee and Muralikumar Anantharaman)

By Anshuman Daga and Cindy Silviana