French PM wants ‘harsh’ punishment for rioters

France's prime minister called on Thursday for "harsh" punishment for those attacking police officers, a day after protesters torched a police vehicle in central Paris.

Protestors shout slogans as they march behind a banner reading:" All united against the labour law" during a demonstration against French labour law reforms in Paris, France, May 17, 2016. REUTERS/Gonzalo Fuentes

"The punishment must be harsh, the enquiry has just started, arrests have been made," Manuel Valls told RTL radio.

A rare rally by police to protest against "anti-cop hatred" descended into violence on Wednesday, with a small group hammering a police vehicle with iron bars before hurling an explosive device inside.

Paris police chief Michel Cadot said the officers "were in the car when the explosive device was thrown inside", an account confirmed by a surveillance video.

The two officers -- one man and one woman -- managed to flee the vehicle.

The incident came as some 300 people defied a ban to march through the streets chanting "Cops, pigs, killers!" as police forced the demonstrators back with volleys of tear gas.

Four suspects were arrested on Wednesday and a fifth was picked up on Thursday, sources close to the investigation said.

Several rallies in recent weeks -- often against controversial labour reforms proposed by the deeply unpopular government of President Francois Hollande -- have erupted in violence.

Small groups of troublemakers appear to have infiltrated the demonstrators and are bent on attacking security forces.

Valls called on the organisers of some demonstrations to prevent troublemakers from mingling with the crowd.

Over the past two months, some 350 members of the security forces have been injured during protests against the proposed labour reforms, which were forced through the lower house of parliament last week without a vote.