French police clashed with striking firefighters on Friday, leaving five people injured after a demonstration against pension reform in the Mediterranean resort of Nice.

Two firemen and three police officers were hurt in the punch-up, and five firemen were arrested, according to officials. One of the protesters needed hospital treatment following the brawl.

Firefighters claimed baton-wielding police had charged into the 200-strong protest unprovoked, but state officials said the firefighters had started the trouble and had also beaten and kicked police.

"We were running about in the square to wind them up a bit, and they just piled in with truncheons," one of the protesters, Fire Sergeant Gilles Morin, told AFP at the scene.

One eyewitness said he had seen police violently batter a fireman. "There were seven around him. One of them kicked him in the head even once he was down," he said, speaking on condition of anonymity.

Police officers insisted that they were responding to an attempt by the firefighters to break through a police cordon, kicking and punching. "It was they who charged the police," one said.

Christophe Marx, chief of staff to Nice's regional prefect, the senior state-appointed official and police chief, said: "This was an intolerable action by an irresponsible fringe group within the Nice fire brigade.

"This violence is completely unworthy of those who wear a uniform," he declared, adding that, as it had not been declared in advance, the firefighter's protest had been illegal from the outset.

President Nicolas Sarkozy's government is trying to push through unpopular reforms to the French pension system in the teeth of fierce opposition from the trade union movement and, in particular, many public sector workers.

Firefighters have been angered at moves to raise their retirement age, arguing that it should remain lower than that of many other workers because of the gruelling and dangerous nature of their jobs.

The Nice brigade has symbolically declared itself "on strike", while still responding to emergency calls.