The head of DGSI, France's intelligence agency, has warned that ISIL's "will" to attack the country is still intact, two years after mass shootings and a suicide bombing in Paris killed 130 people.
With ISIL being rapidly defeated in Syria and Iraq, Laurent Nunez said there were fears for what the return of hundreds of French citizens, who had fought for the extremist group overseas, would mean for security.
"What worries us are plans for terrorist attacks prepared by teams that are still operating in fighting zones in Syria and Iraq," Mr Nunez told French newspaper Le Figaro.
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He said that home-grown attacks were a big concern as ISIL ordered its followers to target their places of origin.
Despite losing ground in the Middle East, Mr Nunez said: "The will of the jihadists to take action is intact."
French prosecutor Francois Molins warned that the "internal" threat from jihadists remained high, with attacks likely.
“We are witnessing a new bout of isolated actions, 11 since the beginning of the year, which supports the idea of an increasing endogenous threat,” Mr Molins told franceinfo radio.
The risk of attacks from individuals using "low tech" methods such as cars and knives was higher than bigger plots using bombs, although bigger terrorist cells remain.
French president Emmanuel Macron paid tribute to the victims of the Paris attacks during a ceremony marking the two-year anniversary of the deadliest act of violence in France since the Second World War.
In a heavily-guarded ceremony, the president joined families of the victims in releasing balloons to honour their loved ones.
Meanwhile, Mr Macron is faced with a dilemma over what to do with jihadists with French citizenship who attempt to return to the country.
Speaking in Abu Dhabi last week, he said those individuals, who include widows and children of dead ISIL fighters, would be assessed on a case-by-case basis.
French authorities have estimated that about 690 French nationals, including 295 women, are still in Iraq and Syria.
"A majority doesn't want to come back to France given the legal proceedings they face upon their return. But some women, widows, with their children, are inclined to travel back," Mr Molins said.
"We should not be naive. We are dealing with people who are more 'disappointed' than 'sorry'."
