TOKYO • Toshiba's top executives were behind a plan that inflated profits by US$1.2 billion (S$1.64 billion) over the past six fiscal years, according to an independent panel, in a stinging indictment of one of Japan's best-known firms.

The amount is almost triple the 55 billion yen (S$606 million) writedown the Tokyo-based company estimated earlier.

The findings, declared yesterday, came after Toshiba hired an outside team of investigators to look into irregularities uncovered by securities regulators probing its balance sheet earlier this year.

This is the country's biggest business scandal since camera and medical-equipment maker Olympus Corp's 13-year cover-up of US$1.7 billion in losses blew up in late 2011.

Toshiba has lost $3.6 billion in market value since May 8, when it withdrew its earnings forecasts, cancelled the year-end dividend and widened the accounting probe.

Chief executive Hisao Tanaka and his predecessor, vice-chairman Norio Sasaki, were aware of the overstatements of profits and delays in reporting losses in a corporate culture that "avoided going against superiors' wishes", the panel said in a summary report filed by Toshiba to the Tokyo Stock Exchange.

Mr Tanaka is scheduled to hold a briefing today.

The accounting irregularities are believed to have affected its mainstay infrastructure-related, semiconductor, television and personal computer businesses.

Toshiba has not been able to close its books for the latest year because of the probe, which also forced the company to cancel its annual dividend.

This is its second probe in less then two years.

In October 2013, it announced it had found that subsidiary Toshiba Medical information Systems had overstated results for several years.

REUTERS, AGENCE FRANCE-PRESSE