Nicolas Maduro, Venezuela's vice president, has said President Hugo Chavez is suffering from "new complications" following his cancer surgery in Cuba.
Maduro did not give details on Sunday about the particular issues, which he said came amid a respiratory infection. He said Chavez's condition remains "delicate".
Maduro delivered a televised address from Cuba, where he was visiting the sick 58-year-old leader. He held up a copy of a newspaper confirming that his message was recorded on Sunday.
Below a picture of 19th century independence hero Simon Bolivar - the inspiration of Chavez's leftist Bolivarian Revolution movement - the vice president spoke with a solemn expression alongside Chavez's eldest daughter, Rosa, and son-in-law Jorge Arreaza, as well as Attorney General Cilia Flores.
Maduro had arrived in Havana on Saturday in a sudden and unexpected trip to visit Chavez. He said on Sunday that he would remain in Havana "for the coming hours" but did not specify how long.
Officials have said that Chavez already suffered unexpected bleeding caused by the six-hour operation for an undisclosed form of cancer in his pelvic area.
His resignation for health reasons, or his death, would upend the politics of the South American OPEC nation where his personalised brand of oil-financed socialism has made him a hero to the poor but a pariah to critics who call him a dictator.
Al Jazeera's Teresa Bo, reporting from Buenos Aires, said, "Chavez wanted Maduro to transmit to the people his best wishes [and the fact that] his condition was being treated with the right medicine."
But Maduro's comments suggest an increasingly bleak outlook for the ailing president.
Medical experts say that it is common for patients who have undergone major surgeries to suffer respiratory infections and that how a patient fares can vary widely from a quick recovery in a couple of days to a fight for life on a respirator.
Maduro's latest update differed markedly from last Monday, when he had said he received a phone call from the president and that Chavez was up and walking.
The Venezuelan leader has not been seen or heard from since undergoing his fourth cancer-related surgery on December 11, and government officials have said he might not return in time for his scheduled January 10 inauguration for a new six-year term.
"The president gave us precise instructions so that, after finishing the visit, we would tell the [Venezuelan] people about his current health condition," Maduro said.
"Thanks to his physical and spiritual strength, Comandante Chavez is facing this difficult situation," Maduro said.
Maduro expressed faith that Chavez's "immense will to live and the care of the best medical specialists will help our president successfully fight this new battle". He concluded his message saying: "Long live Chavez."
Maduro said he had met various times with Chavez's medical team.
According to the Venezuelan constititution, if Chavez is not reinaugrated by the January 10, as is scheduled, then the president of congress will take over and call for new elections in 30 days.
However, Diosdado Cabello, President of Venezuela's National Assembly, has said that inaugration ceremony will be postponed if Chavez will not attend it.
Before Chavez left for Cuba, he acknowledged the precariousness of his situation and designated Maduro as his successor, telling supporters they should vote for the vice president if a new presidential election was necessary.
"There would be a big sympathy vote for the Chavez-chosen candidate," said Colin Harding, Latin American Affairs Specialist. He added that Maduro would be assured a solid vote.
Harding told Al Jazeera that he did not expect the relationship with the US to improve at all under Maduro. "It is possible that he would be less confrontational than Chavez."
"Once Chavez is off the scene, almost everything changes in Venezuela and it is extremely hard to predict what might happen."