Venezuelan President Hugo Chavez is being treated for a "respiratory deficiency" following a severe lung infection, Information Minister Ernesto Villegas has said.
The statement read out on television on Thursday night ends days of speculation on the nature of his condition.
Mr Villegas explained: "Chavez has faced complications as a result of a severe respiratory infection.
"This infection has led to respiratory deficiency that requires Commander Chavez to remain in strict compliance with his medical treatment."
The government also condemned what it termed "psychological warfare" regarding the president's condition following fresh cancer treatment in Cuba and urged Venezuelans not to listen to rumours.
Opposition figures have seized on his recent illness to try to push for Mr Chavez to be declared unable to continue in office, which would trigger a new election within 30 days.
However the Supreme Court would be likely to make any final decision.
As Aslef's annual assembly of delegates begins in Edinburgh tomorrow the general secretary explains the challenges his members - and workers across the country - face