French PM urges unions to scrap violence-marred protests

France's prime minister urged labour union leaders on Thursday to call off anti-reform protests, saying turnout was waning but violence on the fringes was mounting.

As crowds gathered for nationwide marches in opposition to labour law reforms, Manuel Valls said that ultra-violent gangs of "people who want to kill a cop" were hijacking otherwise legitimate protests in order to attack the police.

"Union leaders need to live up to their responsibilities," he said. "If rioters turn up at each and every protest it's time to ask whether some of these protests are worth it," he said in a radio interview on a new days of strikes and demonstrations.

French train services were slashed by more than 50 percent in many cases by a second straight day of strikes, while truck drivers continued to blockade strategic parts of the country's road network, notably near oil refineries.

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

CGT chief Philippe Martinez said ahead of this week's wave of protests that it was time to "move up a gear" with rolling strikes and marches to force the government into retreat.

Police estimates put turnout at 68,000 nationwide in a first of this week's street protests on Tuesday, which while slightly higher than one a week earlier was significantly smaller than peak-levels of more than 300,000 in late March.

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".

Defending police, who are already working overtime to ensure heightened security after the deadly Islamist attacks on Paris last November, Valls singled out an incident on Wednesday where two officers were forced to flee their patrol car when it was surrounded by an angry crowd and torched in central Paris.

Some of the perpetrators of the attack may, he said, include some who had been banned from the streets by a Paris police prefect before a judge struck down that prohibition order.

The issue that has put the labour unions on the warpath is a one of the flagship reforms of President Francois Hollande's term, a change of labour law that would make hiring and firing easier. Hollande has said he will not withdraw it.

More than 300 police have been hurt and protestors have also complained of injuries sustained in seemingly isolated cases of police brutality.