Apple is facing an investigation by the US Securities and Exchange Commission (SEC) to determine whether the firm misled investors over the state of chief executive Steve Jobs's health, according to a Bloomberg report.

Jobs's physical condition has been a subject of deep concern for Apple shareholders, as the company's stock has fluctuated dramatically with each new revelation.

His gaunt appearance at last year's Worldwide Developers Conference led to a statement of reassurance from Apple in January that Jobs was not suffering from a resurgence of pancreatic cancer.

Jobs said at the time that he was suffering from a hormone imbalance, and would take a six-month leave of absence from the company. However, it emerged last month that Jobs had undergone a liver transplant.

Bloomberg said that the SEC will want to know what Apple's board of directors may have known when Jobs said that his illness was the result of hormone problems.