Calling on the police to "continue the dialogue" with Interior Minister Bernard Cazeneuve and Justice Minister Jean-Jacques Urvoas, Valls said they should "respect the rules", which ban them from demonstrating while on duty or in uniform, as some have done over the last three days.
Following demonstrations in the Paris region, Marseille and Nice on Tuesday evening, there were more protests late on Wednesday, in central Paris, Nancy in the east and Toulouse in the south.
Sparked by a firebomb attack that has left a police officer fighting for his life and three others wounded, the protests have given voice not only to concerns about violence but also about understaffing and an alleged lack of resources to fight crime.
Politics and police
Valls also turned on the right-wing opposition, which accuses the government of being soft on law and order.
"Politically exploiting this movement is not dignified," he told a press conference, going on to accuse former president Nicolas Sarkozy of reducing police numbers when he was in office.
Sarkozy, who hopes to stand for president again next year, called the charge "lies".
Although the figure that has been bandied about of 7-10,000 police posts being cut during his presidency is exaggerated, there were some 2,000 fewer police officers at the end of his second term, according to LCI television.
National Front accuses government of hating police
The National Front (FN) has denied involvement in the demonstrations after Socialist Party national secretary Jean-Christophe Cambadélis said he detected the far-right party's "hand" in their "lawless" aspects.
"No 'hand' but unconditional support faced with a government that manifestly hates the police," FN vice-president Florian Philippot responded, while party leader Marine Le Pen called the discontent "healthy" and "legitimate".
Tax relief on bonuses
The police complain not only about being understaffed but of being overstretched by the fight against crime and ongoing anti-terror operations.
Cazeneuve has promised a consultation process to establish their needs to be followed by improvements in equipment and working conditions in 2017.
MPs on Thursday voted to grant tax relief for bonuses, estimated to be worth 1-2,000 euros a month, paid to soldiers and CRS riot police involved in the Sentinelle anti-terror programme.