A French police officer is in a critical condition and three others were injured after a firebomb attack on their vehicles by a group of youths in a Paris suburb.

The 28-year-old male officer suffered "very serious burns on the hands and the entire body", local prosecutor Eric Lallement said.

The officer's 39-year-old female partner also suffered severe burns and the two others suffered light injuries.

The attack occurred on Saturday 8 October when a group of around 15 youths swarmed around their cars in the town of Viry-Chatillon and hurled firebombs.

Director of the national police Jean-Marc Falcone said: "We believe that it was organised and premeditated."

The officers were on a patrol near a housing estate, where there had been a series of carjackings at a traffic junction, local media reported.

Prime Minister Manuel Valls said the culprits would be "relentlessly pursued and brought to justice. "At a time when the security forces are bravely responding to (terrorist) threats facing our country, such intolerable acts call for exemplary sanctions," Valls said.