Her security is among the highest in the country and this is a great concern to us

Kumbh Mela organiser Jiwesh Nandan

Italian-born Mrs Gandhi, dressed in a red sari, performed a ritual prayer, and then stepped into the water at the sacred confluence of the Ganges, Yamuna and mythical Saraswati rivers.

The Congress party, which Mrs Gandhi leads, said the visit was a "personal decision", although it has been criticised by her opponents as a political ploy.

The Kumbh Mela - the biggest mass event in the Hindu calendar - takes place once every 12 years and this year's festival is expected to draw 30 million devotees, who believe that bathing in the waters will wash away their sins.

Security arrangements

Mrs Gandhi's dip into the waters attracted cries of support from some nearby pilgrims who shouted: "Long Live Mother Ganges! Long Live Sonia!"

Millions have been drawn to the holy waters

Later, she had an audience with the head of one of Hinduism's leading religious orders, Swami Swaroopanand.

The local authorities were less enthusiastic about her trip.

The Kumbh Mela organiser, Jiwesh Nandan, said she had been asked to postpone her visit because it would coincide with the run-up to one of the most important bathing days on 24 January.

"We have tightened arrangements as far as possible - but her security is among the highest in the country and this is a great concern to us because we cannot isolate areas for her movement," Mr Nandan said.

Congress tradition

Critics have linked the visit to the fact that elections are due in the politically-important state of Uttar Pradesh, where the festival is taking place.

But Mrs Gandhi told journalists that her trip was religious, not political.

The Congress Party said it was a tradition started by India's first prime minister, Jawaharlal Nehru, and continued by his daughter Indira Gandhi.

Sonia Gandhi married Indira's son Rajiv, but he was assassinated in 1991.

As a result, she is one of the most heavily-guarded figures in Indian public life.

Mrs Gandhi has been trying to restore the fortunes of the Congress party since its poor performance in national elections in 1999.