NEW DELHI: Indian Congress leader Rahul Gandhi's sister clashed with an estranged cousin running in the election on an opposition ticket on Tuesday, in a new sign of aggression that partymen hope will draw her deeper into active politics to revive their fortunes.

Priyanka Gandhi, two years younger than Rahul, is seen as a more natural leader in the hurly-burly of Congress than her brother who has often seemed remote and is struggling to stave off a likely heavy defeat in the five-week vote.

She told reporters on the campaign trail in her brother's constituency that she could not forgive her cousin Varun for fighting the election as a candidate of the Hindu nationalist Bharatiya Janata Party that her party reviles.

The BJP's Narendra Modi has won support on promises to jumpstart a flagging economy and sweep out the Nehru-Gandhi dynasty that has ruled India for most of the period since independence in 1947.

“This is not a family tea party. It is an ideological war. (I) would not have forgiven my child, if he did something like this,” she said in Amethi, northern India, as Varun registered as an opposition candidate in a neighbouring constituency.

Those comments brought to the fore a long-running estrangement in India's most famous political dynasty whose every move is watched by India's billion-plus population and which remains intensely secretive.

Varun is the son of Sanjay Gandhi, the younger of former prime minister Indira Gandhi's sons who died in an air crash in 1980. Rahul and Priyanka are children of the elder son and former minister Rajiv Gandhi, who was assassinated by a Tamil suicide bomber in 1991.

Varun's mother fell out with Indira Gandhi soon after her husband's death and later was a minister in a BJP government.

"Heart of India"

“This election is a fight for the heart of India,” Priyanka said, echoing the Congress campaign that a possible BJP administration led by Modi, seen as a deeply polarising figure, would be damaging to India's secular foundations.

Varun hit back at his cousin saying she had crossed the lines of decency, television channels reported.

Priyanka's comments come amid persistent calls from Congress elders that she play a greater role in reviving the fortunes of the 129-year-old party that an opinion poll suggested on Monday was set for a spectacular defeat.

Priyanka has repeatedly said she will only campaign in the constituencies of her mother and party chief Sonia and her brother Rahul and there had been no change in that position, a Congress spokesman said on Tuesday.

“The media is trying to make a big issue of it. She has said so many times her role is limited to the two constituencies. We should respect that decision,” spokesman Shakeel Ahmed said.

But clamour for the charismatic Priyanka who bears a striking resemblance to Indira has risen at each election. This election, party insiders say, she has spent more time at Rahul's campaign headquarters.

Rasheed Kidwai, a journalist who has written a biography on Sonia, said Priyanka appeared to be playing a greater role than previously, helping Rahul plan his campaign and acting as the bridge to the old guard, some of whom have been ruffled by his team.

“It's not a question of Rahul or Priyanka. It will probably be Rahul and Priyanka given the scale of the challenge that the Congress faces in the election and beyond.” The BJP was dismissive, saying the Congress party's faith in one dynasty was the cause of its undoing.

“The family charisma has faded away...The real solution to the problem is to make Congress a more structured party. The Congress party solution is, if one incumbent in the family fails, the alternative can only be another member of the family,” senior leader Arun Jaitley wrote in a blog.