TOKYO (REUTERS) - Japan's SoftBank Group is close to finalising an investment in US office-sharing startup WeWork, in a deal expected to be worth over US$3 billion (S$4.21 billion), CNBC reported on Monday (Feb 27).

The investment under discussion is a US$2 billion primary tranche of funding, followed by a secondary round worth more than US$1 billion, CNBC reported, citing a source.

SoftBank may increase the size of the secondary investment to nearly US$2 billion for a total investment of almost US$4 billion, CNBC added. If the deal closed, We Work, which provides shared workspaces largely to start-up companies, would be valued at more than US$20 billion.

SoftBank and WeWork declined to comment.

Led by founder Masayashi Son, SoftBank has made a string of surprising acquisitions and investments over the past months, most recently an all-cash deal to buy asset manager Fortress Investment Group.

Son is steering SoftBank, a diverse company that holds stakes in US carrier Sprint, Chinese e-commerce giant Alibaba and other firms, towards cutting-edge tech investments as the telecoms services markets mature.

As part of that gameplan, SoftBank bought UK chip designer ARM Holdings, Britain's most valuable technology company, for US$32 billion, and announced with Saudi Arabia the planned creation of an investment fund that could grow up to US$100 billion.

Son also promised a US$50 billion investment and 50,000 new jobs in the United States after meeting US President Donald Trump in early December.

Some of SoftBank's moves have caused concern among analysts, as it is wrestling with a heavy debt pile.