Such assertions have been met with disbelief by opposition leaders, who say that a man who is too sick to appear or speak to the nation cannot be capable of leading.

Even some Chávez supporters have voiced skepticism. When officials said a major currency devaluation announced this month had been approved by Mr. Chávez directly, they showed a signed document to prove it.

“If he was sick, how did he sign it? That’s what doesn’t convince me,” said José Alberto Fernández, an ardent Chávez supporter who sold plantains on a street corner a few blocks from the military hospital. He said he did not have faith in Mr. Maduro or the other officials running the government and was elated to have the president back on home soil. “We need a leader,” he said.

Beyond orating, singing, reciting poetry and lecturing on television for hours at a time, Mr. Chávez would communicate to the nation through Twitter. But even that fell silent soon after he was re-elected to another six-year term on Oct. 7. On Monday, however, his account was suddenly active again.

“We have arrived again in Venezuela,” said the first of three posts, which appeared at 3:42 a.m. “Thank you, my God!! Thank you, beloved people!! We will continue treatment here.”

Later, Mr. Maduro announced that Mr. Chávez had surpassed four million followers on Twitter after his posts went up on Monday. Then on television, he presented a 20-year-old woman, Rosnaty Jiménez, and identified her as the president’s four millionth Twitter follower, saying her prize would be a new home and a new job for her mother.

Mr. Chávez’s health remains the biggest question mark. His return raised the question of whether he will now be sworn in for the new term that started on Jan. 10, while he was incommunicado in Cuba. His absence for the start of his term set off a constitutional controversy, but the Supreme Court said he could be sworn in later.