|Kirchner was the incumbent secretary-general of the South American grouping Unasur [AFP]
Nestor Kirchner, the former president of Argentina and husband of the incumbent Cristina Fernandez-Kirchner, has died.
Kirchner, who was the secretary-general of the regional grouping Unasur (the Union of South American Nations), died of a heart attack at a clinic in the city of El Calafate, southern Argentina, on Wednesday.
He was taken to the clinic after suffering chest pains. He had undergone treatment for a heart problems earlier this year, including two major operations. In September 2010 he suffered a heart attack.
His family was reportedly with him when he died.
Kirchner, 60, was expected to run for the presidency in 2011 to replace his wife.
The Brazilian government declared three days of official mourning following Kirchner's death. Luiz Lula de Silva, Brazil's president, said that Kirchner had been "a big ally and fraternal friend".
"His role was important in the economic, social and political reconstruction of his country. And his will for the fight for South American integration."
Barack Obama, the US president, also offered his condolences in a statement.
Argentine's were massing outside the Casa Rosada, the presidential palace in the capital, with a mass gathering planned for Wednesday night.
"There will be a demonstration to honor Kirchner and to show Cristina that we're with her, supporting her," Emilio Persico, the leader of the Evita Movement, said.
"In these days we'll be demonstrating in the streets that we are millions who will replace Kirchner."
Kirchner was also serving as a National Deputy of Argentina - a congressman - for Buenos Aires province at the time of his death.
He was Governor of Santa Cruz - the province where El Calafate is located and where the Kirchners own a ranch - from 1991 until 2003.
He then served as president from 2003 to 2007, and is widely credited with pulling the country out of economic catastrophe after it committed the biggest ever default on World Bank and international loans.
A ceremony is expected to be held in Rio Gallegos, the capital of Santa Cruz and Kirchner's birthplace, before his body is brought to Buenos Aires, the national capital, on Thursday.