Interrupting a period of political and popular unity unseen since the end of the second world war, Ms Le Pen said immigration offered fertile ground for radical Islam, and criticised Europe and its “dogma of free movement” for benefiting terrorists.

 “Whether from the right or the left, one French administration after another has failed to size up the problem of the task to be accomplished,” she wrote in Monday’s New York Times, in an apparent attempt to make political capital from the attacks.

Ms Le Pen’s comments come as polls show François Hollande, who was France’s most unpopular president before the attacks on satirical weekly Charlie Hebdo and a Jewish supermarket, has emerged stronger from the crisis.

A poll from Ifop-Fiducial released by Paris Match on Monday suggested that Mr Hollande’s approval rating had soared by 21 percentage points, to about 40 per cent. The improved sentiment towards the president has even extended to his handling of the economy, with 24 per cent of those polled judging it positively, up by 7 percentage points. The approval rating for Manuel Valls, prime minister, rose 17 points to 61 per cent.

Pollsters and political analysts have had a difficult time predicting whether the National Front will gain from the terror attacks, carried out by radicalised French citizens. But Dominique Reynié, head of Fondapol, a right-leaning think-tank, said the tough stance adopted by Mr Valls over the attacks may have “taken oxygen away“ from the far-right party.

In the New York Times article, Ms Le Pen pointed to the “tons of weapons from the Balkans enter French territory unhindered” every year and how “hundreds of jihadis move freely around Europe”.

“The massive waves of immigration, both legal and clandestine, our country has experienced for decades have prevented the implementation of a proper assimilation policy,” she wrote.

Measures suggested by Mrs Le Pen include stripping French-born jihadis of their citizenship, although she did not detail the legal means to implement such a measure. Police control should be reinstated at national borders, she also said, which would run against the principles of the European Schengen area.

Speaking on the France Inter radio station, she also warned that radical Islam was undermining France’s secularism. “The rise of the veil, the requests within companies for prayer areas . . . that is the emergence of fundamentalism,” she said.

France’s political dynamic will be tested in two weeks’ time with a legislative by-election in Doubs, in eastern France, to fill the seat left vacant by Pierre Moscovici, the Socialist former finance minister who is now EU economy commissioner. Local elections are also set for March and December.

Nicolas Sarkozy’s UMP party is expected to win the Doubs seat in the second round against the National Front, which attracted more than a third of the votes in last year’s European elections there.

Defeat for Mr Hollande’s Socialists would see them lose their absolute majority in parliament, which would mean the party having to rely more on the Green party to pass laws. Highlighting how important the Doubs by-election has become, Ms Le Pen, Mr Valls and Mr Sarkozy are all expected to campaign there.

The Financial Times