Paul McCartney
Sir Paul McCartney is in hospital receiving treatment for a mystery

Sir Paul McCartney has called off his entire Japan tour after falling sick.

The former Beatle cancelled his concert in South Korea next week after reportedly being struck down by a mystery virus.

In a statement released by Hyundai Card, the organizers for his South Korea concert McCartney said: "I was really looking forward to visiting and playing in South Korea for the first time and I'm sorry to be letting fans down. I'm very disappointed by this and hope to be able to visit soon."

The statement added that "'Paul is still not feeling better and this cancellation is unavoidable," but the organisers declined to comment on his illness.

McCartney has been treated at Tokyo's St Luke's International Hospital, where third wife Nancy, 53, has remained at his bedside.

The singer's fans have been gathering outside the hospital awaiting news of the idol's condition.

Doctors have now ordered the star to take "complete rest" while he recuperates.

McCartney's personal spokesman insisted that there is no cause for concern stating: "He will make a complete recovery and has been ordered to take a few days rest. Paul has been extremely moved by all the goodwill messages he has received from fans all over the world," he added.

A message on the legendary star's website stated that McCartney was upset about the cancellations. "He has been doing all he can to get better. He has only ever had to reschedule a handful of shows in his entire career. He hates to let people down."

Fans will be offered a refund on the tickets, which range from about $55 to $290.

McCartney was scheduled to perform at a Seoul stadium on May 28. It would have been his first concert in South Korea.

The veteran rocker is also scheduled to perform in the U.S., where he'll appear in concert at several venues over two months.

Both his UK and US publicist declined to give any more details of the star's illness.