President Hugo Chavez of Venezuela has suffered "new complications" after a cancer operation in Cuba.
In a televised address from Cuba, Vice-President Nicolas Maduro said Mr Chavez continued to be in a "delicate state".
Mr Chavez underwent a fourth cancer operation on 11 December in Cuba, but suffered a respiratory infection.
The president - who has been in power since 1999 - is due to be sworn in on 10 January for another six-year term.
The BBC reports Mr Maduro gave no details about Mr Chavez's condition, but said the latest complications were connected to the respiratory infection.
"We have been informed of new complications that arose as a consequence of the respiratory infection we already knew about," he said.
"The president gave us precise instructions so that, after finishing the visit, we would tell the (Venezuelan) people about his current health condition.
"The state of health of President Chavez continues to be delicate."
He added that the treatment was "not without risk."
A BBC correspondent in Havana said it is now three weeks since Mr Chavez has been seen or heard from in person.
There are also many questions about what will happen on 10 January when Mr Chavez is due to be re-inaugurated.
National Assembly head Diosdado Cabello recently said that the swearing-in ceremony would be delayed in the case of Mr Chavez's absence.
However, opposition leaders say postponing the inauguration would be unconstitutional.
The constitution states elections must be held within 30 days if there is an "absolute absence" of the president.