The 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.
He 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, told the Journal du Dimanche newspaper she had been "harassed for an hour" by an unnamed interior ministry official on the phone after a "commissioner" came to see her the day after the attack.
She said she had been told to detail the presence of the local police at the Bastille Day fireworks event and also to report "that the national police had also been deployed at two points".
"The national police were perhaps there, but I couldn't see them on the video," Bertin told the newspaper.
"He ordered me to put in (the report) the specific positions of the national police which I had not seen on the screen," she was quoted as saying.
On Thursday, the left-leaning Liberation daily reported that only one local police car was barring the entry to the pedestrianised seafront when Mohamed Lahouaiej Bouhlel forced his lorry onto the Promenade des Anglais, mowing down families.
Since the carnage 10 days ago -- 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.
Order to erase video
The furore was further fuelled by a request from prosecutors that security camera videos of the night of the attack be erased.
Local authorities claimed it amounted to "destruction of proof" but prosecutors, who already had a copy, said it was to stop "shocking" images of the events -- in which 350 people were also hurt -- leaking out.
Former Nice mayor Christian Estrosi, who now heads the regional administration, has also accused the government of lying over the number of police and soldiers protecting the crowds that night.
The head of the national police Jean-Marc Falcone joined the fray Sunday by taking the unusual step of calling a press conference to declare that "the manipulations attacking the national police, its leaders and its minister must stop".
President Francois Hollande was forced on Friday to say that he still had "full confidence" in Cazeneuve, a key member of his government, promising "truth and transparency" on the security measures that were in place.
Cazeneuve's office categorically denied Sunday that he had sent a representative to the local Nice police, "contrary to what Madame Bertin claims". Francois Molins, the Paris anti-terrorist prosecutor who is leading the investigation, told AFP he had sent two officers to talk to police in the Nice video unit on July 15 as part of his inquiry.
Cazeneuve called the claims "undignified" and pointed the finger at Estrosi, hinting that he had orchestrated "daily attacks" on him even though he was also partly responsible for security in Nice.
But the far right National Front weighed in saying "the minister gave the impression that he was trying to stop the truth" leaking out in what they claimed was becoming "a state scandal".
And Nice MP Eric Ciotti, an Estrosi ally from the same opposition Republicans party, said the policewoman's testimony was "another element which shows that something is not transparent".