TOKYO (Reuters) - Hong Kong-based activist fund Argyle Street Management asked Japan's Toshiba Corp 6502.T on Thursday to exit more non-core businesses such as office machinery company Toshiba TEC 6588.T to bolster margins of the once-mighty conglomerate.

FILE PHOTO: The logo of Toshiba Corp is seen behind cherry blossoms at the company's headquarters in Tokyo, Japan April 11, 2017. REUTERS/Toru Hanai

Toshiba has already announced exits from its British nuclear power and U.S. LNG businesses as part of a plan to regain investor confidence after a 2015 accounting scandal uncovered widespread irregularities and forced it to recognize huge cost overruns at its now-bankrupt U.S. nuclear unit Westinghouse.

“We believe that further firm commitments to divest other non-core businesses (such as Toshiba TEC for instance), would be well received and affirms management’s commitment to decisive execution of its plans,” the investment fund said in a letter sent to Toshiba CEO Nobuaki Kurumatani and shown to Reuters.

The fund also reiterated its call for the company to boost share buybacks to 1.1 trillion yen ($901.5 million), calling its current 700 billion yen repurchase launched in November “grossly insufficient”.

Toshiba had substantial excess capital, and a higher buyback would make sense “especially with the current depressed share price of Toshiba”, the fund said.

It also called on the company to hire more board members with international experience.

“As a long-term shareholder of Toshiba, we may feel the need to propose an agenda item at the AGM next year should we feel that our suggestions have not been given due consideration,” the fund said.

Toshiba could not immediately comment.

It was not immediately clear how much stake Argyle owned in Toshiba.

Argyle had previously opposed Toshiba’s sale of its chip business to a Bain Capital-led group, saying the deal undervalued the prized unit. The sale was completed earlier this year.