A radicalized French teenager had been planning to carry out a knife attack at a popular weekend spot for families and tourists, investigators said.

The 15-year-old, already on a high-security threat list, was arrested on Saturday, one week after French police prevented an attack in central Paris by a group of female Islamic State followers who tried to blow up a car filled with gas bottles.

French Prime Minister Manuel Valls warned on Sunday that the terrorist threat was at its “maximum” level and said France’s security forces were “foiling attacks every single day.”

The unnamed youth was arrested at his home near the Coulée Verte, a “green corridor” walkway in Paris similar to New York’s High Line, where detectives allege he was planning to stab random passers-by last weekend.