PARIS (AFP) - French Prime Minister Manuel Valls revealed on Thursday that five terror attacks had been "foiled" in France since 2013.

He told radio station France Inter that "numerous attacks had already been foiled - five if you take into account the attack which happily did not take place at Villejuif" on the outskirts of Paris.

A 24-year-old Franco-Algerian IT student is being held by police investigating an alleged plot to attack a church near the French capital.

His plans were exposed after he accidentally shot himself and police uncovered a stash of weapons and detailed plans to attack the church.

Police said his DNA was also linked to the murder of a young mother in Villejuif who was found shot dead in the passenger seat of her car on Sunday.

The revelations over the planned attack come less than four months after an extremist killing spree in Paris left 17 people dead, leaving France on high alert.

"The threat has never been as high. We have never had to face this kind of terrorism in our history," Valls told France Inter.

Hundreds of French nationals have joined extremist ranks in Iraq and Syria, accounting for almost half the European fighters there, according to a report released this month by the upper house Senate.

Valls said 1,573 French citizens or residents had been implicated in "terror networks", 442 of which were currently believed to be in Syria and 97 of whom had died there.

"I want to remind you that seven French citizens have died while carrying out suicide attacks in Syria or Iraq," Valls added.