Last month, Toshiba became the target of a potential takeover bid and other bids could be forthcoming.

Investment banks have pitched to Toshiba's independent directors for an advisory role, the people, who could not be named as the information has not yet been made public, told Reuters.

A UBS spokesman in Japan declined to comment.

Toshiba also declined to comment specifically on the appointment of UBS, but said in a statement to Reuters that the appointment of advisers would help increase the transparency around its decision-making.

"The board is independently appointing financial and legal advisers, and will strategically consider ways to increase our corporate value from an independent standpoint," it said in an emailed statement.

One of the sources said that UBS will also communicate with Toshiba shareholders. It will have a separate role from Goldman Sachs, which is an activist defence adviser for Toshiba's management team.

An announcement of the appointment could be made as soon as Friday at Toshiba's earnings briefing, the person said.

Toshiba has faced calls from its leading shareholders to explicitly seek offers from potential suitors and undergo a strategic review following a $20 billion buyout bid from CVC Capital Partners last month.

The future ownership of Toshiba, however, remains uncertain after CVC later said it would "step aside and await guidance" from the company after the Japanese conglomerate dismissed the bid as lacking in substance.

U.S. buyout firm Bain Capital is also considering a bid to take Toshiba private, Reuters reported last month, and has entered discussions with banks to secure funding for its potential deal. Bain had declined comment.

KKR & Co Inc and Canada's Brookfield Asset Management are also interested in Toshiba, sources have said. KKR and Brookfield had previously declined to comment on reports of potential bids.

A senior executive at one of Toshiba's main lenders said last month that several private equity funds had contacted his bank for potential financing to take the company private, but no talks are in progress.

CVC had approached Bain about a joint bid before its offer was made public but Bain was not interested, the first person said.

Bain has successfully tackled a major complex deal that involves Toshiba.

In 2017, it led a consortium with partners including South Korean chipmaker SK Hynix and Apple Inc to win an intense and long-fought battle for control of Toshiba's chip unit, now called Kioxia Holdings.

Toshiba retains around 40% of Kioxia.

(Reporting by Makiko Yamazaki in Tokyo and Kane Wu and Scott Murdoch in Hong Kong; Additional reporting by Takashi Umekawa; Editing by Sumeet Chatterjee and Susan Fenton)

By Makiko Yamazaki, Kane Wu and Scott Murdoch