Sonia Gandhi
Sonia Gandhi (center) Reuters

Sonia Gandhi, India's most powerful politician, has cancelled what would have been her first public address since undergoing surgery for an undisclosed illness, highlighting speculation about her ability to run the ruling Congress party.

Gandhi was due to appear at the Wednesday rally in Uttarakhand against a backdrop of mounting media speculation that she might be about to hand the reins of power in the Congress party to her son, Rahul.

Newspapers have said this could happen within weeks. She has been running viral fever since yesterday and that's why she could not make it for the rally, Congress party spokesman Janardan Dwivedi told Reuters. Her speech would be read out by a Congress representative, he said.

The 64-year-old Gandhi's return would have effectively kicked off her party's campaign in a string of state elections next year. Those include Uttar Pradesh, a state of 200 million people that is likely to be key to her party's fortunes and whether it can return to power in elections in 2014.

One of the party's star campaigners, Gandhi's gathering was meant to be a show of force in Uttarakhand, a state governed by the main opposition Bharatiya Janata Party (BJP).

Gandhi's illness has come as the coalition government has struggled to fend off street protests against corruption scandals that have plagued Prime Minister Manmohan Singh's second term in office. Her condition remains the subject of speculation.

India's media usually keeps a respectful distance from the personal life of the Gandhi family, which has ruled the country for much of its independent history. But some reports said that she underwent treatment at New York's Sloan-Kettering Cancer Centre.

Gandhi underwent successful surgery in August and devolved part of her responsibilities to Rahul, who was criticised for dithering during the corruption protests and, unusually, was jeered at a public appearance.