The 79-year-old maestro has undergone "a complex operation,"according to KP, and his doctors are "seriously worried" about his condition. Currently only his closest relations and associates are allowed to visit him; a special exception was made for President Vladimir Putin on Tuesday.

Employees of the Blokhin Center told KP that Rostropovich is now undergoing what they described as a conservative course of treatment. "We hope to avoid an additional operation," the report quotes unnamed specialists as saying.

The paper adds that Rostropovich was rushed to Moscow's Central Hospital on December 28 for an aggravated ulcer; he was not discharged until January 5.

The Associated Press asked the conductor's Moscow spokesperson, Natalia Dollezhal, about the KP report; she declined to comment.