France's justice minister is defending specialized prison units for Islamic radicals after a recent attack on guards, saying the units see less violence than the rest of the overcrowded French prison system.

Jean-Jacques Urvoas said Tuesday on France-Inter radio that he will not close the five units around France that group together Islamic radicals, despite complaints from prison workers' unions after two guards were injured in Osny north of Paris.

Urvoas said that kind of attack is "intolerable," but "paradoxically" there are fewer such attacks in radical units than others.

Urvoas spoke from a prison in the Paris suburb of Fresnes, where he is announcing plans Tuesday to create more spaces in prison to tackle overcrowding, a decades-old problem that has gained new attention amid the country's state of emergency.