In a speech on Sunday to supporters of her National Rally party in the southern town of Frejus, Le Pen said her party would campaign for May's European Parliament elections "in liaison" with allies in its Europe of Nations and Freedom party.

France's president Emmanuel Macron has pitched the vote as an open battle between anti-immigrant populists like the National Rally and pro-European Union progressives like himself.

"In France, our objective is to beat Macron," she said to a chorus of cheers in the southern bastion of far-right support.

"In Europe, it is to build with our allies, the other (nationalist) groups, a majority that makes a break from the decaying European Union and moves towards a cooperation of nations which respect each other's diversity and identity."

Le Pen wants to force Brussels to hand back powers to nation states, an outcome supporters of the EU say would sound the death knell for Europe's political and monetary union.

Europe's populists have scored election successes from Italy to Sweden and from Austria to Hungary, yet uniting the eurosceptic parties may prove difficult.

Previous attempts to unite the far right have produced little and Le Pen offered no new answers, reiterating her vision of a Union of European Nations whose member states would cooperate but regain their national sovereignty.

Le Pen has struggled to unite her party and assert her leadership since she was soundly beaten by Macron in last year's presidential run-off vote.

A poll last week of voter intentions for the May election showed Le Pen's party gaining ground to stand neck-and-neck with Macron's centrist LREM.

On Sunday she attacked Macron's first 16 months in office, but saved her toughest words for France and Europe's immigration policy and praised Matteo Salvini, Italy's anti-immigrant interior minister.

"With us, France will once again control its borders," she said.