Sonia, widow of assassinated former prime minister Rajiv Gandhi, has been attacked for her foreign birth by the ruling Hindu nationalists in the election that ends in just over a week.

After playing down the issue of who would be prime minister for most of the campaign, the Congress now says there is no other contender in the grand old party.

Television exit polls from the first three rounds of voting up to Monday said Congress, helped by hectic campaigning by Gandhi and her daughter, Priyanka, and son, Rahul, had made strong gains although it still trailed the ruling Bharatiya Janata Party-led coalition.

"If the Congress gets majority on its own, Sonia Gandhi will be prime minister," said party spokesman Abhishekh Manu Singhvi.

Two more rounds of voting, including in the giant heartland state and key to power in Delhi, Uttar Pradesh, are due next Wednesday and May 10.

Birth no issue

Congress, which ruled for decades after independence from Britain in 1947, could win anything from 190 to 210 seats, along with its allies, far more than the 140 seats held now.

The Hindu newspaper said the exit polls had shown Gandhi's Italian birth was not an issue with most voters despite attempts by the BJP to whip up emotions.

Gandhi, who took Indian citizenship after her marriage into the celebrated Nehru-Gandhi family, says she does not care about the BJP attacks.

The BJP-led coalition has said it would introduce legislation barring anyone born overseas from holding high public office if it wins, a move critics say primarily targets Gandhi.

Under the constitution, any Indian citizen can run for the top office.