PARIS: Masked youths clashed with police officers and set fires in cities across France Tuesday as protests against a proposed hike in the retirement took an increasingly radical turn. President Nicolas Sarkozy pledged to crack down on “troublemakers” as clashes between youth and police broadened, saying he would ensure that “public order is guaranteed.” More than 200 protests and one-day strikes by workers in sectors across the French economy were planned around the country over a bill raising the retirement age to 62. Initial estimates from the SNCF national railway operator and the Education Ministry suggested the number of public sector strikers was diminishing after week of disruptions by refinery workers, students and train staff that have snarled traffic, left drivers without gasoline and canceled hundreds of flights. In many cities, protesters were being joined by young people who appeared to be seizing an opportunity to lash out at police. At a high school in the Paris suburb of Nanterre, closed because of earlier violence, a few hundred youths started throwing stones from a bridge at nearly as many police, who responded with tear gas and barricaded the area. It was not immediately clear if there were injuries or arrests. Youths also knocked an Associated Press photographer off his motorbike and kicked and punched him as they rampaged down a street adjacent to the school. Nanterre has often seen student protests in past years and the latest clashes were reminiscent of 2005 riots that spread through poor housing projects nationwide with large, disenfranchised immigrant populations.