A Spanish newspaper is reporting that ailing Cuban leader Fidel Castro is in "very grave" condition after three failed operations.

Castro is suffering complications from the intestinal infection diverticulitis, which involves the formation of pouches on the outside of the colon, Spain's El Pais newspaper reported.

The newspaper cited two unnamed sources from the same hospital, Madrid's Gregorio Maranon hospital, which sent a surgeon to Cuba in December to examine 80-year-old Castro.

Cuba has released little information on Castro's condition, but the newspaper reports paint a bleak picture.

It says that when the surgeon visited Castro in December, he had an abdominal wound that was leaking more than a half-litre of fluids a day, causing severe loss of nutrients.

The report said the Cuban leader was being fed intravenously.

Dr. Jose Luis Garcia Sabrido, the Madrid hospital's chief surgeon who flew to Cuba in December, could not be reached for comment Tuesday.

But Sabrido is reportedly standing by his opinion that Castro is recovering from stomach surgery despite the report.

Sabrido's secretary said the surgeon has not changed his prognosis that Castro is slowly recovering after treatment, according to Reuters.

A Cuban diplomat in Madrid also disputed the newspaper report, saying it was "an invented story."

"It's another lie and we are not going to talk about it. If anyone has to talk about Castro's illness it's Havana,'' said the diplomat, who spoke on customary condition of anonymity.

"It's an invented story. I don't know anything about this," he told AP.

Castro temporarily handed power to his younger brother and designated successor, Raul, in July.

Castro disappeared from public view after taking ill in July, prompting rampant speculation on the revolutionary's condition.

Then in December, Castro was absent from a manor military parade marking 50 years since his return from exile, an absence that stunned many Cubans.

The U.S. has speculated Castro is suffering from cancer, a suggestion rejected by Sabrido.

Some U.S. doctors have said they think Castro is suffering from diverticular disease, which can cause bleeding in the lower intestine, especially in people over 60.

The speculation was bolstered by the El Pais report, which said Castro had suffered a bout of the disease.

"In the summer, the Cuban leader bled abundantly in the intestine,'' El Pais reported. "This adversity led him to the operating table, according to the medical sources. His condition, moreover, was aggravated because the infection spread and caused peritonitis, the inflammation of the membrane that covers the digestive organs.''

The newspaper said Castro's did not recover well from the first operation, in which surgeons extracted part of his large intestine. The report also said he developed peritonitis, a potentially fatal inflammation of the abdominal cavity's lining.

A second operation to clean and drain the infected area also failed, further impeding his recovery, the paper said.

He was then struck with inflammation of the bile duct that blocked secretion of digestive enzymes into the small intestine, El Pais said.

Sources told the newspaper Castro was fitted with an artificial bile duct made in South Korea, which failed, and was then replaced with one made in Spain.

A statement attributed to Castro was released on New Year's Eve saying his recovery was "far from being a lost battle.''