French far-right leader Marine Le Pen was attacked from all sides over Europe as presidential candidates went head to head in the second live TV debate.
The centrist candidate Emmanuel Macron said Ms Le Pen's nationalist proposals amounted to "economic warfare".
But she was also accused from the right of not being tough enough on France's membership of the EU.
Francois Fillon, meanwhile, said that France needed Europe when up against the US and China.
Ms Le Pen, leader of the National Front (FN) party, promised to restore control of France's borders and scrap the euro, or else hold a referendum on EU membership.
Speaking alongside 10 other candidates as things got a little heated in the second of three televised French presidential election debates, she said that her presidency would improve the lives of French citizens.
France holds its first round of voting on 23 April. Unless one candidate wins more than 50% of the vote, the two leading contenders will go to a second round on 7 May.
Mr Macron, the frontrunner, accused Ms Le Pen of lying, and said that "nationalism is war".
"You are saying the same lies that we've heard from your father for 40 years," he said.
Ms Le Pen, who also came under attack from conservative candidate Mr Fillon, retorted: "You shouldn't pretend to be something new when you are speaking like fossils that are at least 50 years old."
Meanwhile, nationalist right-wing outsider Francois Asselineau said that he was "the only true candidate of Frexit", and promised to trigger Article 50 - the process to start the country's divorce from the EU - immediately if he were to win power.
Watching the debate: BBC's Hugh Schofield in Paris
The debate was extended to include the six minor candidates, so inevitably it is on the six minor candidates that water-cooler conversation is going to focus.
On Jean Lasalle - "son of a shepherd, brother of a shepherd" - with his impenetrable Pyrenean accent; on Francois Asselineau with his "Frexit" obsession; on the rival Trotskyites Philippe Poutou and Nathalie Arthaud with their rousing calls to punish the bosses.
Some of it was diverting, some of it was deadly serious. But after a while you realised that there were really only two people out there who were in any sense defending - more or less - the way things are. Those two are Francois Fillon and Emmanuel Macron.
Everyone else - from Marine Le Pen to the uber-Gaullist Nicolas Dupont Aignan to the firebrand of the left Jean-Luc Melenchon (as brilliant as ever on stage) - wants the rules of Europe and the economy totally rewritten.
Small wonder this first round boils down to a fight between Mr Fillon and Mr Macron. It is a fight for the chance - in round two - to stand up for the existing order against the anti-system.
Read more on this story
Turning the topic to security, Ms Le Pen said that France had become a "university for jihadists", prompting angry interruptions from the left-wing candidates.
Most polls suggest that Ms Le Pen and Mr Macron will face each other in the second round run-off.
However, Tuesday's debate gave Mr Fillon, 63, an opportunity to close the gap on the leaders.
Mr Fillon was the frontrunner in the campaign until he was hit by the "fake jobs" scandal and placed under formal investigation. He is accused of paying hundreds of thousands of euros to his family for work they did not do.
He was trailing third in the first round, according to polls, a position which would eliminate him from the race.