"Sonia Gandhi remained in the ICU (intensive care unit) for 24 hours and has thereafter been moved out," Congress Party spokesman Janardan Dwivedi said in a statement.

The name and location of the hospital where Gandhi was being treated has not been released but India's Tehelka news magazine said on microblogging site Twitter that Gandhi was at New York's Memorial Sloan-Kettering Cancer Center.

A report in the Indian Deccan Herald newspaper, citing medical sources, said Gandhi, 64, had undergone surgery for cervical cancer.

Dwivedi said the Gandhi family was grateful for all the get-well messages sent to the Congress leader, adding she was likely to return to the country in the next two to three weeks.

The Congress Party broke the surprise news of Gandhi's impending surgery on Thursday and has since blocked all queries regarding the nature of her illness.

The Italian-born Gandhi is the widow of assassinated former premier Rajiv Gandhi and wields enormous clout from her power-broking position as Congress party president.

In her absence, she has appointed a four-member group to handle the day-to-day running of the Congress Party -- including her son Rahul Gandhi, tipped as a future prime minister.

The Nehru-Gandhi dynasty has exerted huge influence in India during most of its post-independence history, with three members of the family becoming prime minister.

Sonia Gandhi holds total sway within the Congress Party and is credited with crafting the strategies that gave it back-to-back general election wins in 2004 and 2009.

Her illness means she will miss a crucial session of parliament for the scandal-plagued government which intends to introduce draft laws on a range of key areas, including corruption, land acquisition and food security.

Gandhi, who has described herself as "a reluctant politician," took charge of the party in 1998.

Copyright AFP (Agence France-Presse), 2011