Singer Linda Ronstadt has cancelled the remainder of her US tour after undergoing surgery for a mystery ailment. The 60-year-old star was due to perform in Texas and Mexico - but was forced to pull out in order to have the surgery. And she refuses to give details of what the surgery is for, although cancer has been ruled out. Ronstadt's agent SHELLY SCHULTZ said, "It wasn't an emergency, but it came about rather quickly, so she decided to do it sooner rather than later. It's surgery, it's completed, and she's fine." Ronstadt hit the headlines recently after launching a scathing verbal attack on US President George W Bush, calling him an "idiot" and "immoral".