The Paris prosecutor has announced harsher prison sentences for returning French jihadis, saying the country faces an increased risk of attacks as the Islamic State group weakens in Iraq and Syria.

Francois Molins, whose office is in charge of terrorism investigations, told Le Monde newspaper on Friday that around 700 people from France are fighting for extremist groups in Iraq and Syria and "at one moment or another we will face the return of a large number of French fighters and their families." He said his office will hand down more severe criminal charges, with possible sentences up to 30 years, in cases that might previously have drawn maximum sentences of 10 years.

Molins said there were 26 terrorism cases in 2013, while today his office is following 324 cases.