“For all of Venezuela, it creates a considerable amount of uncertainty,” he said.

After weeks of speculation that Chávez’s health had taken a turn for the worse, the president traveled to Cuba on Nov. 27 to undergo hyperbaric oxygen therapy. While there, he said, inflammation and soreness led doctors to perform additional tests that found the “malignant” cells near the site of his original cancer.

The administration has never said what type of cancer the president has, or what organs might be affected. But the problem was first announced in June of last year, when a somber Chávez told the nation he’d had a “baseball sized” tumor removed from his pelvic region. Since then, he has had at least two more surgeries and undergone several rounds of chemotherapy and radiation treatment.

In February, he announced that his cancer had returned, but during the campaign he said he had beaten the illness.

On Sunday, Ramon Guillermo Aveledo, the national director of the opposition coalition, said the administration’s secrecy had led to “unrest and uncertainty.”

“Nobody knows for sure what is real and what is not,” Aveledo said at a news conference. “Hiding information for the benefit of some, at the expense of national interests, is not democratic and doesn’t produce good results.”

Chávez has not said when he will go to Cuba or how long he will stay. But on Sunday, the National Assembly unanimously approved his temporary absence.

In power since 1999, Chávez won his fourth consecutive presidential bid Oct. 7, with 55 percent of the vote, versus Capriles’ 44 percent. Chávez has said he would use the next six years to deepen his socialist reforms, which have included free healthcare, education and housing — but also mass expropriations and price controls that have scared off foreign investment.

At the Caracas rally, many of his supporters were unwilling to talk about life after Chávez.

“We’re here to show him our support as he leaves for Cuba,” said Jose Gregorio Lucero, a community educator. “He doesn’t have to worry while he recuperates — and comes back for the inauguration on Jan. 10.”

Staff Writer Jim Wyss reported from Bogotá and Special Correspondent Andrew Rosati contributed to this report from Caracas.