French officials denounced Thursday an "unacceptable" attack on two police officers who were shot and had their guns stolen while they were carrying out a surveilllance operation in a Paris suburb.

One of the officers was in critical condition after being shot four times, while the other was shot twice after they were dragged out of their unmarked car and beaten late on Wednesday. "They were pulled from the car and set upon, then shot and had their service weapons stolen," said Ludovic Collignon of the Alliance police union.

The mayor of Herblay, where the attack took place, said three people managed to grab the officers' guns and shoot them. "I don't think they realised they were police," Philippe Rouleau told BFM television. "In the middle of the fight the attackers seized their weapons and shot them point-blank."

Interior Minister Gerald Darmanin described an act of "unheard-of violence," promising on Twitter that "everything will be done to find the culprits".

"It's an unacceptable tragedy, and obviously I hope those responsible will be arrested and face trial," Justice Minister Eric Dupond-Moretti said on BFM.

Several politicians seized on the attack to accuse the centrist government of President Emmanuel Macron of failing to tackle crime, in particular in tough neighbourhoods of the sprawling Paris suburbs.

Valerie Pecresse, the rightwing president of the Ile-de-France region surrounding the capital, said on Twitter the "ultraviolent attack should remind all those who forget that enforcing the law is a commitment that puts your life at risk".

"What will it take for the government to take this problem seriously and announce a massive crackdown on crime?" tweeted far-right leader Marine Le Pen.

A study last November by France's national crime observatory (ONDRP) found that 6,002 police agents were wounded in 2018, a 16 percent jump from the previous year, the largest increase since 2009.

Of these, 666 officers were wounded by guns, knives or other weapons, compared with 418 in 2017.