Steve Jobs resigns as Apple chief executive

The company said he would be replaced by Tim Cook, who was the firm's chief operating officer and had been standing in for Jobs during his medical leave.

It said Jobs, who underwent a liver transplant for pancreatic cancer in 2004, had been elected as Apple's chairman.

Apple's shares fell 7% in after-hours trading.

The company has yet to give a specific reason for the 56-year-old's resignation, but he addressed a letter to the Apple board of directors and Apple community.

He wrote: "I have always said if there ever came a day when I could no longer meet my duties and expectations as Apple's CEO, I would be the first to let you know.

"Unfortunately, that day has come. I hereby resign as CEO of Apple. I would like to serve, if the Board sees fit, as Chairman of the Board, director and Apple employee.

"As far as my successor goes, I strongly recommend that we execute our succession plan and name Tim Cook as CEO of Apple.

"I believe Apple's brightest and most innovative days are ahead of it. And I look forward to watching and contributing to its success in a new role.

"I have made some of the best friends of my life at Apple, and I thank you all for the many years of being able to work alongside you."

Jobs had begun a third period of medical leave from the chief executive's post around eight months ago.

He founded Apple in 1976 along with Steve Wozniak and Ronald Wayne.