Venezuela’s President, Hugo Chavez, is suffering from “complications” brought on by a “severe lung infection” which developed after surgery, officials say.
Mr Chavez, 58, had his fourth operation for cancer in Cuba on 11 December and then developed a respiratory infection.
In a statement from Caracas, Information Minister Ernesto Villegas said the infection had “led to a respiratory insufficiency”.
Mr Chavez is due to be sworn in for another term in office on 10 January.
“[Mr] Chavez has faced complications as a consequence of a severe lung infection,” said Mr Villegas.
The president has not been seen in public since having cancer surgery in Havana, prompting persistent speculation about his condition.
The information minister was among a number of Mr Chavez’s political allies who have urged people not to believe what they called lies about his health.
Mr Villegas warned Venezuelans not to be taken in by a “psychological war” being fought in the media which had the “ultimate aim of destabilising the Bolivarian republic”.
Vice-President Nicolas Maduro and National Assembly Head Diosdado Cabello were among several dignitaries to have visited Mr Chavez this week.
Mr Maduro said on Wednesday that President Chavez was “conscious” and had gripped his hand firmly as they discussed Venezuelan politics.
He and Mr Cabello flew back to Caracas on Thursday and dismissed rumours of a split in the governing socialist movement.
“We’re more unified than ever,” Vice-President Maduro said upon his return to Venezuela from Cuba.
“We swore in front of Commander Chavez that we’ll be united at the side of our people,” he said.
Opposition activists have speculated about a split between Mr Maduro, whom President Chavez named as his preferred successor, and Mr Cabello, who the constitution decrees should temporarily take over power if the Venezuelan leader were to have “an absolute absence”.
Mr Cabello said that those who were spreading rumours about problems between him and Mr Maduro would “have to wait 2,000 years for that to happen”.
Mr Chavez has been in power since 1999 and was elected for a fourth term in office in October.
It is unclear if he will be able to attend the swearing-in ceremony for another six-year term in office next week, nor what the procedure would be if he was unable to attend.
Mr Cabello recently said that the ceremony could be delayed. But the opposition says such a move would be unconstitutional.
Opposition politicians say there have been no independent reports of the president’s condition.
On Thursday, Caracas Mayor Antonio Ledezma demanded that a commission travel to Cuba to report back on Mr Chavez’s health.