(CNN) -- Venezuelan President Hugo Chavez is battling a "severe" lung infection that has caused respiratory failure, a top official said.
Chavez, 58, has been hospitalized in Cuba since undergoing cancer surgery more than three weeks ago.
He is following a strict treatment regimen for "respiratory insufficiency" caused by the infection, Venezuelan Information Minister Ernesto Villegas said in a televised statement Thursday night.
The information minister did not provide details about the treatment or prognosis.
"It is something quite serious in many cases," said Dr. Elmer Huerta, an oncologist and past president of the American Cancer Society.
While officials have previously mentioned the respiratory infection and described Chavez's health situation as delicate, Thursday night's statement was notably different from past government announcements, Huerta said.
"Of the 20-some statements they have given, this is the first one that really mentions key medical words," he said.
The phrases "severe lung infection" and "respiratory insufficiency," he said, "say a lot about the delicacy of President Chavez at the moment."
Chavez has not been seen publicly since his surgery, and officials have not specified what kind of cancer he is battling. They first revealed that the Venezuelan president had a respiratory infection more than two weeks ago. At the time, Villegas said the infection had been controlled. On Sunday, Venezuelan Vice President Nicolas Maduro said "new complications" had surged as a result of the infection.
According to the National Institutes of Health, "the outlook for respiratory failure depends on the severity of its underlying cause, how quickly treatment begins and ... overall health."
The condition occurs when not enough oxygen passes from the lungs into the blood, or when the lungs cannot remove carbon dioxide from the blood properly, the institutes' website says. It can require oxygen therapy or the help of ventilator for treatment, according to the NIH.
After revealing the new medical details Thursday night, Villegas was quick to decry what he said was a "psychological war" that international media have unleashed "with the ultimate goal of destabilizing Venezuela."
He said there was "iron unity" among the Venezuelan government, the military and the country's people "concerning the leadership and political ideology of Comandante Hugo Chavez."
Dr. Elmer Huerta, American Cancer Society
The Venezuelan information minister's comments Thursday night came hours after Maduro and another top Chavez ally accused opposition leaders of organizing a campaign to spread rumors about the Venezuelan president's health.
Standing side by side on the floor of a coffee factory in Caracas, Maduro and National Assembly President Diosdado Cabello sharply criticized the opposition in remarks broadcast on state-run VTV.
"Don't fall victim to the opposition's rumors. ... They have bad intentions every time they talk," Cabello said.
Maduro said opposition claims that officials have been withholding information are baseless, noting that authorities had released dozens of communiques about Chavez's health in the past 22 days.
On Wednesday, opposition leader Ramon Guillermo Aveledo called on the government to release more details about Chavez's health situation and his prognosis.
"Secrecy is the source of the rumors that increase uncertainty and cause anguish," he told reporters.
On Thursday, Cabello and Maduro said Chavez's supporters are united.
"The Chavistas, we know what we are going to do in any circumstance that happens in this country. ... We will not betray the people. We will not betray the workers. ... To the contrary, every day there will be more revolution," Cabello said.
Amid the uncertainty, the U.S. government is talking to "Venezuelans from across the political spectrum," Victoria Nuland, a State Department spokeswoman, said Thursday at a news briefing.
But she stressed that "any political transition that takes place in Venezuela has to be the product of decisions that are made by Venezuelans. There's no made-in-America solution here."
Asked about the Venezuelan opposition's calls for more information about Chavez's condition, Nuland said, "We don't have any way to evaluate what's being said, but we have seen concern within Venezuela that the government's not being transparent."