Hundreds of jihadi militants have returned to France from Iraq and Syria, France’s interior minister said on Sunday.

In an interview with French newspaper Le Journal du Dimanche, Gerard Collomb said that an estimated 271 radical Islamists who fought for militant groups have returned from war zones after being members of the Islamic State militant group (ISIS).

The figure is made up of 217 adults and 54 minors, some of whom are in French detention, and all of whom are under security services surveillance, Collomb told the paper. The minister could not provide a precise figure on how many French nationals had been killed in Iraq and Syria, but estimated that as many as 1,900 French nationals were involved in radical Islamist activities in Iraq and Syria, according to interior ministry data as of mid-2016.

The minister said the threat of a militant assault on French soil remained “very high,” with authorities foiling seven plots already this year. A key concern of the French counter-terror forces, he said, was a homegrown radical being directed “remotely” by ISIS or Al-Qaeda figures in the Middle East.

The country is battling the most serious case of homegrown extremism in the European Union, with around 15,000 suspected radical Islamists on the watch-lists of French authorities, overseen by the country’s Counter-Terrorism Coordination Unit, with some 4,000 individuals at high risk of committing an attack.

Security services have also prevented several female homegrown jihadis from carrying out attacks, in what represents a new dimension of the threat to the country’s security. Paris prosecutor Francois Molins said last September that “hundreds” of radicalized women could return from Iraq and Syria as ISIS continues to lose territory to ground forces backed by the U.S.-led coalition.

The country has borne the brunt of radical Islamist attacks in Europe, with several mass casualty attacks striking major cities since January 2015. As a member of the anti-ISIS coalition and one of the most liberal countries in the West, France is a top target for jihadi groups.

Shooting attacks on the offices of the satirical magazine Charlie Hebdo and a kosher supermarket in January 2015 were followed by an ISIS cell that launched a suicide bomb and shooting attack across the French capital in November 2015, killing 130 people.

Months after France fell under a state of emergency, which remains in place today, a Tunisian national plowed a high-tonnage truck into revelers watching the Bastille Day fireworks on the promenade of the southern city of Nice.

Several smaller attacks, such as the murder of a priest in northern France and the shooting of a policeman on Paris’ famous Champs-Elysees avenue, have since taken place.

The failure of Francois Hollande’s Socialist government, replaced by centrist Emmanuel Macron in June’s election, to tackle security led to a corresponding surge in support for Marine Le Pen’s far-right National Front party that spouted anti-immigrant and anti-Islam rhetoric.