Liza Minnelli has cancelled a string of concerts this summer due to a mystery medical condition.

The 68-year-old Cabaret singer said she was "devastated" after she was advised by her doctors not to perform or travel for long periods of time. The nature of her medical condition is not yet known.

A concert at London's Royal Albert Hall is one of the cancelled shows.

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Minnelli, the daughter of Wizard of Oz star Judy Garland, has suffered a series of health problems in recent years, most recently undergoing two hip replacements and a new "bionic knee".

A statement on Minnelli's website said: "Liza Minnelli's physicians have advised her not to perform or travel for long periods of time because of a medical condition.

"As a result, her concerts in Europe, which were scheduled for July, have been cancelled.

"We are discussing rescheduling dates at an appropriate time. Liza wants her fans to know she is devastated not to be able to perform right now but will see them soon."

Under the listing for Minnelli's July 2 concert on the Royal Albert Hall website, it says: "Unfortunately this concert has been cancelled due to illness.

"We will be contacting those who have purchased tickets through the Royal Albert Hall to arrange full refunds."

Additional reporting by Press Association