Rousseff's office in Brasilia said her trip to Greece was never confirmed because it overlapped with two events she is due to attend at the United Nations on drugs and climate change.

Rousseff, facing an impeachment effort over a series of scandals and probes in Brazil, had been expected to attend the April 21 torch-lighting event along with Greek President Prokopis Pavlopoulos and the head of the International Olympic Committee, Thomas Bach.

The ritual at the birthplace of the Olympic Games in ancient Greece traditionally marks the countdown to the world's biggest multi-sports event with the lighting of the torch and a torch relay.

"The President of Brazil Dilma Rousseff has cancelled her presence at the event according to information provided to the Hellenic Olympic Committee (HOC) by the embassy of Brazil," event organisers HOC said in a statement.

Rio will host the first Olympics in South American from Aug. 5-21, with their torch relay starting on May 3 in the capital Brasilia and ending in Rio on the day of the opening ceremony.

Preparations for the Games have been hit by the country's worst recession in decades, with organisers racing to save money through a series of last minute cost-cutting measures.

Organisers have also grappled with pollution in waters where sailing and rowing events will be held, and the threat of the mosquito-borne Zika virus that has spread across the continent.

These challenges come as authorities have said they suspect corruption in Olympic-building projects carried out by the same construction and engineering firms charged with graft in a major scandal involving state-run oil company Petrobras.