"No-go zone" is an area in a town barricaded off to civil authorities by a force such as a paramilitary, or barred to certain individuals or groups. It has also been used to refer to areas undergoing insurgency where ruling authorities have lost control and are unable to enforce sovereignty.

An expert on Fox News outraged and baffled members of the French public after listing eight "no-go zones" for non-Muslims in Paris, areas where Islamic rules were followed rather than those of the French.
National Security Analyst Nolan Peterson, who spent two years in Paris a decade ago, told the channel that areas within a ten-minute drive from the Eiffel Tower were comparable with Baghdad, adding that he had seen people wearing t-shirts supporting Osama Bin Laden.
The sentiments were echoed by Nigel Farage, the leader of the Eurosceptic Ukip party in the UK, who said that the zones in Paris matched a rise in the "big ghettos" of Europe.
But PM Valls, who was joined by interior minister Bernard Cazeneuve said: “The authority of the state will be guaranteed. There are no no-go zones” before acknowledging that there are “particularly difficult areas”.
But police unions disagreed with the prime minister.
“Of course there are no-go zones in France where the police cannot intervene and do their jobs in safety,” Denis Jacob from the union Alternative police-CFDT told The Local. “And it’s the same for fire fighters or pretty much any representative of the state.
“The police can’t apply the law in these areas, they are attacked. If the police can’t do their work it’s because there are criminals and delinquents who don’t respect the law.”
“It’s not just a problem with this government it’s a problem with all French governments over the last 20 years. Governments will never admit there are no-go zones because it’s a sign of a failed state."
https://www.thelocal.fr/20150115/are-there-really-no-go-zones-in-paris
https://www.thelocal.fr/20161010/are-there-police-no-go-zones-in-france-the-police-say-yes
http://www.lexpress.fr/actualite/medias/no-go-zones-a-paris-fox-news-desinforme_1642835.html