The leader of France's right-wing Republicans (LR) on Tuesday backed an alliance in snap legislative elections with the far-right National Rally (RN) of Marine Le Pen.

"We need to have an alliance while remaining ourselves... an alliance with the RN and its candidates," Eric Ciotti told TF1 television, setting out a position set to be hugely controversial within his own traditional right-wing party.

Ciotti added that he had already had discussions with Le Pen, a three-time presidential candidate, and RN party leader Jordan Bardella.

Le Pen praised "the courageous choice" and "sense of responsibility" of Ciotti, saying she hoped that a significant number of LR figures will follow him.

She hailed the move as a historic break with the traditional right's refusal to work with the far right in France. The LR traces its history back to postwar leader Charles de Gaulle and is the political home of ex-presidents like Jacques Chirac and Nicolas Sarkozy.

"Forty years of a pseudo sanitary cordon -- which caused many elections to be lost -- is disappearing," Le Pen, how head of RN deputies in the lower house National Assembly, told AFP.

But Ciotti's move, which he said was aimed at creating an "significant" group in the new National Assembly after the elections, risks tearing his own party apart.

"A political party is not just one person," said the head of the Republicans in the upper house Senate Bruno Retailleau.

The LR speaker of the Senate, Gerard Larcher, a heavyweight figure, said he would "never swallow" an agreement with the RN.

"Eric Ciotti is only speaking for himself. He must leave the presidency of the Republicans," added the head of the Republicans in the National Assembly Olivier Marleix.