PARIS (Reuters) - France’s prime minister urged union leaders on Thursday to call off protests against reforms to labor laws, saying turnout was waning but violence mounting as some people were hijacking legitimate protests to attack police.

“Union leaders need to live up to their responsibilities,” Manuel Valls said in a radio interview as fresh demonstrations drew hundreds of thousands of people.

“If rioters turn up at each and every protest it’s time to ask whether some of these protests are worth it.”

He singled out an incident on Wednesday when two officers were forced to flee their patrol car when it was surrounded by a crowd and torched in central Paris, describing the attackers as “people who want to kill a cop”.

The government says about 1,300 arrests have been made during weeks of protests which have been joined by a youth movement called Nuit Debout (Night Rising). More than 300 police have been hurt and protesters have complained of injuries sustained in seemingly isolated cases of police brutality.

President Francois Hollande has said he will not withdraw plans to reform labor laws to make hiring and firing easier, which he says will encourage firms to recruit and combat an unemployment rate above 10 percent.

Truck drivers continued to blockade strategic parts of the road network on Thursday and train services were reduced by more than 50 percent by a second straight day of strikes.

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Asked whether some protests could be broken up by police, Valls said attempts to cut off oil refineries and food supply depots could not be tolerated for much longer.

Valls aimed his plea primarily at leaders of unions such as the hardline CGT, saying the number of legitimate protesters was waning after more than two months of demonstrations, some marred by violence.

CGT chief Philippe Martinez said ahead of this week’s protests it was time to “move up a gear” with rolling strikes and marches to force the government to climb down.

Thursday’s turnout appeared to have surged despite the prime minister’s claim, with the police saying 129,000 people took to the streets nationwide, about twice the number they reported at similar demonstrations on Tuesday and a week ago.

Police said they arrested 115 people, taking the total over weeks of skirmishes to almost 1,500. Thursday’s arrests included 19 individuals seeking to tamper with the subway train network in Rennes and 66 in Nantes, both hotspots in Western France.

Riot police, who have repeatedly clashed with masked youths hurling petrol bombs and paving stones, staged a protest of their own on Wednesday to highlight what they described as a surge of “anti-cop hatred”.

Police are already working overtime to ensure heightened security after Islamist attacks on Paris last November and face the task of keeping millions of soccer fans safe when the country hosts the Euro 2016 tournament next month.

The CGT union, whose estimates are systematically three or four times higher than those of police, said 400,000 people took part in Thursday’s protest and more protests would be organized despite the prime minister’s claims that protests were waning.