Paris (AFP) - French far-right leader Marine Le Pen pledged Friday she would campaign for France to leave the EU unless Brussels agreed to return full powers to control immigration and economic policy to member states.

The presidential candidate has promised if elected in May to dump the euro and organise a Brexit-style referendum on France's membership in the European Union.

But recently she has appeared to soften her stance, saying a "common currency" could coexist with the national unit.

Addressing a gathering of foreign correspondents, the National Front (FN) leader insisted she had "not changed my mind."

If she won the vote on May 7, she would immediately begin negotiations with the EU on restoring "four fundamental types of sovereignty: territorial, economic, monetary and legislative".

The discussions, she said, would focus on her demands for the return of intra-EU borders, an end to the primacy of EU over national law, and the right for France to toss out the euro and adopt a policy of "economic patriotism".

Six months later she would put the outcome to a "Frexit" in/out referendum.

"Either I will have secured the return of those four sovereignties and I will advise the French to remain in a new Europe of nations, or I will not and then I will advise them to leave the EU," she vowed.

The anti-immigration Le Pen is one of the top contenders for the presidency, buoyed by anger with elites and concern over migration accentuated by a series of jihadist attacks -- factors that fuelled Britain's decision to quit the EU and Donald Trump's rise in the United States.

Le Pen said the British and US results heralded the "grand return of the nation state".

Most polls show her qualifying for -- but losing -- the run-off second round of the election in May against the conservative candidate Francois Fillon.

But a survey Thursday indicated another candidate, ex-banker and former economy minister Emmanuel Macron, was gaining ground.

The Elabe poll of 995 people conducted on January 3-4 showed the 38-year-old prodigy pipping Le Pen for a run-off spot in two of eight scenarios tested by pollsters.

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France's presidential election remains difficult to forecast, with the final line-up of candidates including the Socialist party contender still unknown.

On Friday, the apparent frontrunner Fillon brushed off criticism of his recent remarks on his Catholic faith.

Asked about the impact on the poor of his planned spending cuts, he told TF1 television Tuesday that as "a Christian" he would "never take a decision that would run counter to the respect of human dignity".

That remark drew an indignant response from his rivals, who accused him of disregarding France's strict laws on the separation of church and state.

"I am who I am, I'm open," Fillon told French channel BFMTV, arguing: "You have to be sincere."

- 'A free woman' -

Polls last year showed French voters were opposed to exiting the EU but were more conflicted about the common currency.

Le Pen said Brussels had used the euro in negotiations with bailout recipients such as Greece and Portugal like "a knife that you stick in a country's ribs to force it to do what its people don't want to do."

She insisted, however, she had "never been hostile to the return of a form of common currency".

The FN leader cited the European Currency Unit (ECU), a pre-euro basket of currencies, as a model for a unit of account among EU members.

Le Pen, like Trump, has also been a vocal supporter of Russian President Vladimir Putin.

On Tuesday, she declared that Russia's 2014 annexation of the Crimean peninsula from Ukraine was "not illegal", having been put to a referendum that Ukraine and the West slammed as a sham.

Her remarks come amid concern over whether Russia may seek to influence other elections following US claims that Russian hackers attempted to skew that vote against Trump's rival Hillary Clinton.

Le Pen, who has struggled to get funding from French banks and is looking to foreign lenders for a loan, declared she would be beholden to no-one.

"I am a totally free woman." she said.

"I don't want France to be subjugated by the US. I also don't want us to be subjugated by Russia."