Apple boss Steve Jobs is to go on indefinite medical leave in order to focus on his health, the company has officially announced.

A press release was issued on Monday afternoon after an email was circulated to all employees. Tim Cook, chief operating officer, will take charge of Apple's day-to-day operations. Jobs insisted in the email that he would still be involved in "major strategic decisions".

Jobs' health has been under scrutiny since he was diagnosed with pancreatic cancer in 2004. After successful treatment, he again took ill in December 2008, requiring a liver transplant in April 2009.

The full text of the release, sent to all Apple employees, follows:

"Team,

At my request, the board of directors has granted me a medical leave of absence so I can focus on my health. I will continue as CEO and be involved in major strategic decisions for the company.

I have asked Tim Cook to be responsible for all of Apple's day to day operations. I have great confidence that Tim and the rest of the executive management team will do a terrific job executing the exciting plans we have in place for 2011.

I love Apple so much and hope to be back as soon as I can. In the meantime, my family and I would deeply appreciate respect for our privacy.

Steve"

Apple is due to announce its FY 2011 Q1 results on Tuesday 18 January.