CARACAS - World leaders mourned on Tuesday the death of Venezuelan President Hugo Chavez, who ruled the oil-rich Latin American nation for 14 years.

On national radio and television, Vice-President Nicols Maduro, picked by Chavez as his successor, described the death of the 58-year-old cancer-stricken president as a "historical tragedy", urging all Venezuelans to unite together.

The sad but not so surprised news came just one day after the Venezuelan government said that Chavez suffered a new and severe respiratory infection, and his health condition remained "very delicate".

In Argentina, President Cristina Fernandez declared three days of mourning and flags to be flown at half mast, and said she would be traveling to Caracas for the funeral.

Brazilian President Dilma Rousseff said Chavez was a "great Latin American" and "friend of Brazil", whose death was an "irreparable loss" to the region.

Meanwhile, leaders of other Latin American countries, including Mexico, Peru, Costa Rica, Colombia, Ecuador, and Nicaragua also sent their condolences.

Also on Tuesday, in a statement released by his spokesperson, UN Secretary-General Ban Ki-moon said he was saddened by the death of Chavez and offered his condolences to the family of the president, the government and the people of Venezuela.

"President Chavez spoke to the challenges and aspirations of the most vulnerable Venezuelans," said the statement.

The late president "provided decisive impetus for new regional integration movements, based on an eminently Latin American vision, while showing solidarity toward other nations in the hemisphere", the statement added.

In Washington, US President Barack Obama said in a short written statement that the United States hoped to improve bilateral ties that were in rocky situations.

"At this challenging time of President Hugo Chavez's passing, the United States reaffirms its support for the Venezuelan people and its interest in developing a constructive relationship with the Venezuelan government," said Obama.

The Venezuelan government, however, demanded on Tuesday two US Air Force attaches leave the country within the next 24 hours, accusing them of espionage.

It believed that one expelled diplomat made unauthorized contact with the Venezuelan military, Maduro said in a televised speech after meeting with the country's civilian and military leadership.

Maduro also accused the "enemies of the country" of inducing the cancer of President Chavez.

He said a scientific commission would be formed and that it would reveal that Chavez "was attacked with the disease".