French President Emmanuel Macron has announced plans for tougher laws to tackle what he called "Islamist separatism" and defend secular values.
In a keenly awaited speech, Mr Macron said a minority of France's estimated six million Muslims were in danger of forming a "counter-society".
His proposals include stricter oversight of schooling and control over foreign funding of mosques.
He had been under pressure to address radical Islam amid security fears.
But his comments were condemned by some Muslim activists who accused him of trying to repress Islam in the country.
Under France's strict principles of secularism, or laïcité, the government is separated by law from religious institutions. The idea is that people of different religions and beliefs are equal before the law.
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IMAGE COPYRIGHTGETTY IMAGES image captionMr Macron's plans include closer scrutiny of Muslim private schools
The country also has the largest population of Muslims in Western Europe. Many complain the authorities use secularism to specifically target them, for instance in banning the hijab.
Speaking outside Paris on Friday, Mr Macron said radical Islam was a danger to France because it held its own laws above all others and "often results in the creation of a counter-society".
He said this form of sectarianism often translated into children being kept out of school, and the use of sporting, cultural and other community activities as a "pretext to teach principles that do not conform to the laws of the republic".
"Islam is a religion that is in crisis all over the world today, we are not just seeing this in our country."
The measures announced by the president will form legislation that will go to parliament before the end of the year.
They include:
stricter monitoring of sports organisations and other associations so that they do not become a front for Islamist teaching
an end to the system of imams being sent to France from abroad
improved oversight of the financing of mosques
home-schooling restricted
Mr Macron also said France must do more to offer economic and social mobility to immigrant communities, adding that radicals had often filled the vacuum.
IImmageAGE COPYRIGHTAFP The speech was the fruit of many months of discussions with religious leaders and intellectuals, says the BBC's Hugh Schofield in Paris. It is being spun by the Élysée Palace as a sign that he wants to talk openly and without embarrassment about the dangers posed by radical Islam.
Many also see the address as an attempt to appeal to right-wing voters ahead of the 2022 presidential election, our correspondent adds.
Islam is increasingly seen as a threat to France's core values in the wake of several terror attacks targeting secular liberties such as freedom of expression.
Last week a man wounded two people with a meat cleaver outside the former Paris offices of the Charlie Hebdo satirical magazine, which the government denounced as "Islamist terrorism". In January 2015, jihadists killed 12 people in and around the magazine's offices to avenge its publication of caricatures of the Prophet Mohammed.
Muslims in France have roundly condemned the violence, and some reacted angrily to Mr Macron's proposals on Friday.
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