"We lament that youths go to jihad, wondering what went wrong. Everything, everything, (Nicolas) Sarkozy and (President Francois) Hollande, you have messed everything up."
Speaking after she won 100 percent of a party vote to remain the unchallenged chief of France's far-right National Front, Le Pen added: "These parties (Sarkozy's UMP and Hollande's Socialists) carry the full responsibility for our situation."
The firebrand politician added: "They accuse those who denounce fundamentalism of being Islamophobes, putting everyone in the same boat and forbidding the slightest criticism of the actions of radical Islam."
More than 1,000 people from a wide range of backgrounds have left France to join the jihadists in Iraq and Syria, with 375 thought to be there currently.
The National Front election came a day after France's main opposition party, the conservative Union for a Popular Movement, elected former president Sarkozy as its leader.
Given Hollande's record unpopularity, many analysts believe the 2017 presidential elections could see Le Pen and Sarkozy facing off in a knockout round.
Since taking the reins of the National Front in 2011, Le Pen has proved herself a wily political operator who softened the xenophobic extremist image the party had held under her father and broadened its appeal.
The party made gains in both local and European elections this year.
Sunday's ballot confirmed Le Pen's firm grip on the party, founded by her father and predecessor Jean-Marie Le Pen.
Reacting to her election, PS secretary of state Thierry Mandon slammed the National Front as a "family business".
"Founded by the grandfather, presided over by the daughter, and now, Marion Marechal Le Pen, the granddaughter and the niece," he said over French radio.
Marine Le Pen's 24-year-old niece was elected to the party's executive committee on Saturday.