CARACAS, Venezuela, Dec 15 - Cuban leader Fidel Castro does not have cancer, but is fighting a "great battle" against a "very serious" illness, Venezuelan President Hugo Chavez said on Friday.

In the most extensive account of Castro's condition following weeks of rumors that he has cancer or is even dead, Chavez said he remained optimistic and that his close ally had been in good spirits when they spoke by telephone on Thursday.

"Some comments have come out, that Fidel has a terminal cancer -- Fidel does not have cancer," Chavez told supporters in a celebration of his December 3 reelection.

"We know you are fighting a great battle," he said, adding that what happened to Fidel was "very serious."

Castro, a close ally of Chavez, temporarily stepped aside in July following intestinal surgery after maintaining more than four decades of resistance to Washington and inspiring a generation of anti-U.S. activists throughout Latin America.

Castro has skipped recent public public appearances including his 80th birthday celebration, and appeared frail and walking with difficulty in video images released in October.

Chavez did not say Castro's health was improving, as he has repeated in recent speeches, but said he was optimistic about his recovery.

"I'm going to send him some chocolate, he likes Venezuelan chocolate," Chavez said. "He's eating, little by little he's feeding himself. We have a lot of faith that those 80 years will become 90, 100 years."

He said last week Castro had not called to congratulate him on his re-election, sending instead a typewritten letter rather than his usual handwritten letters.

Before his surgery, Castro had clung to control over the communist enclave since a 1959 revolution despite a strict U.S. embargo in place since 1962.

U.S. Intelligence chief John Negroponte said in an interview with the Washington Post published on Friday that Castro was near death and had "months, not years" to live.

Chavez, leader of a resurgent Latin American left and heir apparent to Castro's legacy of anti-U.S. activism, has helped undercut the U.S. embargo by providing low-cost oil from Venezuela's bountiful oil fields.

Chavez on Friday unveiled plans to unite numerous parties that support him into a single socialist party, which critics call a sign Chavez wants to follow in Castro's footsteps.

Like Castro in previous years, Chavez harshly criticizes the United States as a decadent empire. He called U.S. President George W. Bush "the devil" in a speech at the United Nations in New York.