The French president pointed not only to potential threats from China and Russia, but also from the United States.
Marine Le Pen said her party would struggle to make payroll following a financial scandal.
If forecasts hold, France's new president will have a large mandate to lead.
Polls predict a landslide victory for French President Emmanuel Macron in the parliamentary elections.
There is a burgeoning divide between the working middle class and the gilded Parisian super-rich.
Since taking over the leadership in 2011, Le Pen has sought to soften her party's far-right image, but for many voters the association remains.
The election now heads into its second round, set for May 7.
French newspaper Libération described the speech as "one of the most hardline of [Le Pen's] campaign so far."
"The problem we have nowadays is this form of low-cost terrorism," the National Front leader said.
Florian Philippot helped give the National Front a softer face—but a younger Le Pen is approaching on the far-right.
National Front leader could be prosecuted for 'publishing violent images.'
The Grand Mufti's office expressed surprise at Le Pen's public reaction to headscarf, claiming she had not expressed concern when informed of the plans prior to the engagement.
National Front leader vows to expel illegal migrants, curb immigration, take France out of the euro zone and levy protective tariffs.
The National Front leader said she did not view the annexation of Crimea as illegal.
The normalization of the National Front's politics means the party is seen as an inevitable contender.
The ascendance of authoritarian and racist parties in Europe are a visceral threat to those whose families survived the pogroms of the past.