A fresh crisis hit France’s government Sunday when a senior policewoman claimed the interior ministry pressured her to alter a report into security at the place were Nice attack took place.

A fresh crisis hit France's government Sunday when a senior policewoman claimed the interior ministry pressured her to alter a report into security at the Nice fireworks display where 84 were killed when a man rammed a lorry into the crowd.

Interior Minister Bernard Cazeneuve -- whose account of police deployments on the night of July 14 celebrations has already faced questions -- has been the lightning rod for criticism over alleged security failures.

Having resisted calls for his resignation from the far right, who are strong in the Riviera city, the Socialist hit back at the "grave accusations" made by the policewoman, saying he would sue for defamation.

Cazeneuve later told France 2 television that he would counter "a villainous campaign" of lies against him from opposition politicians in Nice "blow for blow".

Sandra Bertin, who is in charge of Nice's system of security cameras, said she had been "literally harassed the entire time of writing".

"I was asked to change things and asked to send a modifiable report," she told a media conference.

"Mr Cazeneuve obviously believes I am attacking him personally. I related what happened. Now, it's up to the investigation to determine and prove all that I have recounted."

Earlier, she told the Journal du Dimanche newspaper she had been put under pressure to detail the presence of the local police at the Bastille Day fireworks event and report national police had been deployed at two points.

"The national police were perhaps there, but I couldn't see them on the video," Bertin told the newspaper, adding that she was ordered "to put in the specific positions of the national police, which I had not seen on the screen".

Her lawyer, Adrien Verrier, told the media conference that "if indeed the facts are proven, they qualify as a criminal offence".

On Thursday, the Liberation daily reported only one local police car was barring entry to the pedestrianised seafront when Mohamed Lahouaiej Bouhlel forced his lorry onto the Promenade des Anglais, mowing down families.

Since the Nice carnage -- the third major attack in France in 18 months -- Cazeneuve has also been locked in an escalating row with the right-wing leaders of the Riviera city over claims of slack security.