“We don’t know very much about [Chávez’s] health, there is no official news, only partial reports,” said Chávez critic Teodoro Petkoff, a former presidential candidate and current editor of the opposition newspaper Tal Cual.

Mr. Chávez raised concerns when he said, during a call to a Venezuelan television station two days after his operation, that there were no “malignant” signs found, a former top Venezuelan health official said.

The former official, who asked not to be named, pointed out that a pelvic abscess—a pus-filled cavity that can result from injury or infection—is a reaction to a condition. “His choice of words was a red flag,” the official said.