Venezuelan President Hugo Chavez is responding favourably to treatment for a respiratory infection, the nation's government announced Sunday hours after thousands supporting the cancer-stricken president held rallies across the country.

The rallies came amid complaints by the opposition that it was unconstitutional for the government to indefinitely postpone the socialist leader's inauguration, which had been set for Thursday. The opposition also has been demanding the government provide more information about Chavez's medical condition.

Venezuelan authorities have said Chavez is suffering from a severe respiratory infection that he contracted after undergoing a fourth round of surgery on Dec. 11 in Cuba for a cancer in the pelvic area first diagnosed on June 8, 2011.

Information Minister Ernesto Villegas said Sunday night that Chavez is conscious and responding to treatment for the respiratory infection at a Cuban hospital, although he gave no specifics of Chavez's treatment or condition.

"The respiratory infection is under control," but Chavez "still requires specific measures for a solution to respiratory insufficiency," he said, reading a statement on state television.

"The president is conscious, communicating with his family, his political team and the medical team treating him," Villegas said.

Chavez, who was re-elected Oct. 7, hasn't spoken publicly or been seen since the operation, leading to anxiety among Venezuelans about the country. If he is unable to take office, Venezuela's constitution says new elections must be called within 30 days.

On Saturday, Villegas said that Vice-President Nicolas Maduro, who has been designed by Chavez as his successor, had met with Venezuela's leader since flying to Cuba on Friday.

"Maduro reports that he gave the president a report about the demonstrations of the people's support," Villegas said in a message posted on the Twitter social networking site.

In Caracas on Sunday, Elias Jaua, a close Chavez confidant and former vice-president, urged a crowd of government supporters to "be active in defence of the constitution, in defence of Commander Hugo Chavez's popular mandate."

Opposition plans to challenge inauguration delay

Opposition leaders deny they are trying to stir up violence, insisting they have been careful not to incite unrest even as they oppose the postponement of Chavez's inauguration and say they plan to challenge the move before the Costa Rica-based Inter-American Court of Human Rights.

Jaua nevertheless told state television that some right-wing activists are seeking violent upheaval.

"We know that despite the position that many Venezuelans may have against the revolutionary project, nobody wants to see a fragmented Venezuela, a Venezuela involved in a civil war, that's only what Venezuela's sick right-wingers want," Jaua said.

During a huge pro-Chavez rally last week, Maduro warned that authorities would take action against elected opposition leaders who question the government's legitimacy.

"If you don't recognize the legitimate government of President Chavez, we are evaluating legally very forceful actions," Maduro told tens of thousands of Chavez supporters who filled the streets of downtown Caracas.