Apple said it had found "no misconduct" among existing management staff including Mr Jobs.

But it said the investigation had uncovered "serious concerns" about the behaviour of two former executives relating to options, and would provide details to the Securities and Exchange Commission, the US financial watchdog.

"I apologise to Apple's shareholders and employees for these problems, which happened on my watch," Mr Jobs said.

'Irregularities'

Over 100 firms are undergoing either external investigations - involving the SEC and federal prosecutors - or internal inquiries, to look into the way stock options were granted.

The inquiries centre on the backdating of stock options to increase their value.

The Apple panel found that on 15 dates between 1997 and 2002, stock options "appear to have grant dates that precede the approval of those grants".

Backdating stock options denotes the practice of allowing staff to buy shares at a previous - and lower - price.

This makes it appear like the transaction occurred earlier than it did.

As a result, this allows for stock options to be acquired for less than the current value, which could lead to executives making additional profits when they cash them in..

While backdating is not illegal, it must be clearly accounted for.

Apple - which warned of stock option "irregularities" in June - is now likely to have to amend its past financial statements as a result of the investigation, analysts say.

Fred Anderson, who had been Apple's chief financial officer when the stock options were issued, resigned from the board on the news.

The finding follows the recent decision by the US Senate to launch a hearing into stock options and executive compensation.

Research by Iowa University professor Erik Lie has suggested that almost a quarter of unscheduled options grants made by US companies between 1996 and 2002 were backdated.