Marechal, a popular lawmaker in the former National Front (now known as the National Rally or RN) until she stepped down in 2017 to found a political college, has repeatedly spoken in favour of an alliance between the right and far-right.

During the recent European elections, she pointedly held off calling on voters to back the National Rally (RN), which came out on top with 23.31 percent of the vote.

In a LCI television interview last week, Marechal said she was available to help unite the National Rally with the conservative Republicans, one of the big losers of the European polls, whose leader Laurent Wauquiez quit over the party's abysmal tally of 8.48 percent.

Marechal appeared however to condition her continuing support for the party on its readiness to form such an alliance, even though the Republicans have so far baulked at a tie-up with the far-right National Rally.

"If the RN manages to create alliances that allow it to win the (presidential) election I will have no problem supporting it," she said.

- Far-right has 'not peaked' -

Le Pen, who has built up the National Rally into a major force with a nationalist message with appeal on both the far right and far left, said Friday she "regretted" Marechal's failure to endorse the party.

Le Pen told BFM broadcaster that her niece's view that the far-right could not win power in France by itself and needed a tie-up with the traditional right, was "sad".

The new faultline in French politics, she said, is not between left and right, but between nationalists and "globalists" led by President Emmanuel Macron, whose party came a close second to the RN in the European election, two years after he beat Le Pen for the French presidency.

"The new divide is blowing up the traditional parties. It has blown up the Republicans, in the past it blew up the Socialist Party and it is also blowing up the (hard-left) France Unbowed," Le Pen said.

While Macron's new, centrist Republic On the Move party has been a big beneficiary of the realignment, taking votes both from the right and left, Le Pen said her party also had the capacity to grow further.

"I don't believe we've peaked. Far from it," she said, calling Marechal's view "pessimistic".

The squabbles of the Le Pen family have repeatedly made the headlines in recent years.

In 2015 Marine Le Pen threw her father, far-right patriarch Jean-Marie Le Pen, out of the anti-immigration, anti-EU party he founded in the 1970s for repeating his view that the Holocaust was a mere "detail" of World War II.

But Jean-Marie Le Pen father refused to go quietly, hauling the party before the courts in a series of failed bids to be readmitted.

Marine Le Pen, 50, has been careful to avoid a similar messy spat with her 29-year-old niece, a darling of the party's conservative Catholic old guard.

Last year, Marechal announced she was changing her name from Marion Marechal-Le Pen to simply Marion Marechal.

Le Pen denied any rivalry between herself and her glamorous niece, saying she believed Marechal had no "secret ambitions."

Marechal's television interview however rekindled speculation that she is planning a political comeback, perhaps to succeed her aunt Marine, who was badly weakened by a poor performance in a television debate against Macron in the final round of the 2017 election.