A 18-year-old leftist has been beaten to death by a group of alleged neo-Nazis in central Paris in what French authorities described as a politically motivated attack.

Clement Meric, a student at Sciences Po University, was declared brain dead by doctors at a Paris hospital where he was taken in critical conditions after the assault.

Interior minister Manuel Valls said a dispute between left-wingers and skinheads erupted at a clothes sale in Paris 9th district.

Meric and three of his friends were attending a Fred Perry private sale in the central Rue de Caumartin when a group of four neo-Nazis, including a woman, arrived at the premises.

Eyewitnesses told Le Monde the four sported shaved heads and swastika tattoos; one wore a sweatshirt of British neo-Nazi group Blood and Honour.

Meric, a member of campaigning group Action Anti-fasciste, and his friends reportedly started mocking the skinheads' over their outfit and the subsequent verbal dispute eventually became violent as the two groups moved outside in the street.

Meric was reportedly punched with a knuckle-duster and hit his head on the pavement.

'The horrors of fascism'

He was taken io the Pitié-Salpêtrière hospital and declared brain dead overnight.

The attack was strongly condemned by President Francois Hollande and both left and right political parties.

Far-left parties umbrella group Parti de Gauche blamed Paris neo-Nazi organisation JNR (Young Revolutionary Nationalists) for the killing and called for violent far right organisations to be banned.  JNR founder Serge Ayoub, 48, denied the allegations.

"The horrors of fascism have brought murder to Paris," Parti de Gauch said.

Valls pledged to "eradicate extreme right violence that seriously endangers the republican pact."

The interior minister was later echoed by Hollande, who, on an official visit in Tokyo, said measures against far right groups should be taken if a link between the attackers and an organised movement is proved.

"For too long these groups have created disorder and have to be repressed," Hollande said.

Marine Le Pen, the leader of the far-right mainstream National Front (FN) party, backed the proposal and distanced her party from the crime.

 "FN is not linked in any way whatsoever to this unacceptable and intolerable act," she told RTL radio.

"If it is proven that these groups instruct their members to violence, then the measure [ a ban] can be considered, yes."

READ: Female Skinhead in Neo Nazi Gang Accused of Killing anti-Fascist