Apple's shares fell as much as 5% in the previous session as more questions came to light over its stock-option policy and a spokesman said the company was co-operating with an ongoing investigation.
Apple had to delay the publication of its annual report due to a probe by the Security and Exchange Commission (SEC) investigation and the deadline for this to be presented to the watchdog is Friday.
Apple said in October that it had identified irregularities with regard to how stock options were explained in the past but said no current staff were guilty of any misconduct, however, it focused on the actions of two unnamed former executives and said the way in which they recorded and accounted for stock options had "raised concerns".
A US online journal The Recorder suggested that officials were investigating if Apple altered documents to make options of better value but Apple made no comment.
