PARIS — The fashion is more Brooklyn than Paris, with young Muslims and blacks in low jeans, sunglasses and hoodies, often with a kaffiyeh knotted carefully around the neck, and sometimes, now, with guns. There is a large Jewish community, too, many of them Lubavitcher, with kosher butchers and delicatessens, a large religious school and synagogue, close to the Medina Hammam Center and African grill restaurants like Le Marcory.

The 19th Arrondissement is one of the most fascinating and complicated districts of Paris — one of the largest, youngest, poorest, most racially diverse — and the most criminal. The size of Grenoble or Reims, with nearly 190,000 people, the district, on the northeast edge of Paris, is split into at least three territories, with at least two large mini-ghettos, or cités, run by their own gangs of youths, who spar along the borders and sometimes clash with the Jews. And it borders some of Paris’s poorest suburbs.

This has been a bad month for the 19th, with a surge in violence that has brought anxious responses from community leaders, the mayor of Paris and the police. Six young men have been wounded, another shot to death. And there are new accusations of anti-Semitism, with an attack on three young men wearing skullcaps after an exchange of insults, and the police are adding patrols.

Mendel Shapira, 24, who works in the Eshel Glatt Kosher butcher shop on the Rue Petit, said, “These Arabs and blacks come here because they know Jewish people live here, and it’s worse when there are things going on in Israel.”

Nathalie Ben Simon, 45, is the aunt of Daniel, one of the three young Jews hurt this month, his nose broken in a fight along the Rue Petit. “Three black guys bumped into them for no reason and demanded, ‘Why are you looking at us this way?’ ” she said. “It’s always been a neighborhood that’s a little hot.”

It is also deeply divided, with turf carefully demarcated and monitored by different gangs, some involved in petty theft and drugs. On Saturdays, during the Jewish Sabbath, youth gangs, including gangs of young Jews, migrate to the park of Buttes Chaumont and squabble over territory. Sometimes the insults and battles that begin there are finished later on the Rue Petit, said Morad Chahrine, who directs the J2P social and cultural center.

“It’s less about anti-Semitism than fights among gangs of youths, who create alliances of one district against another,” Mr. Chahrine said, noting the influence of American movies on the styles and habits of the gangs. “This idea of identity of territory starts with economic reasons. This is the youngest and poorest arrondissement in Paris, with a lot of unemployment, and that explains a lot.”

Dominique Sopo, president of the group SOS-Racisme, which works against discrimination, said, “We’re faced with a layer cake, a logic of territorialization.”

He noted that the segregation of the district was not diluted by the public schools, because there is only one nontechnical high school and many Jews are leaving the public schools. “When you live only with your own kind, you build yourself in opposition to the territory next door, in opposition to those who do not have the same origin,” he said. “It’s a caldron that gives rise to high tension, and it’s in this framework that anti-Semitic attacks can be explained.”

The deputy mayor of the district, Adji Ahoudian, in charge of youth affairs, said the decrease in “social diversity” was leading to “confrontation for confrontation,” with a troubling new element, “the commonness of firearms of large caliber, that young people from 15 to 25 are using.” Separate communities and schools, he said, mean that “the kids don’t know each other and that creates a logic of rivalry.”

The atmosphere is especially delicate because of the beating in June of a young Jew, Rudy Haddad, 17, who was put into a coma by a gang of black and Arab youths. President Nicolas Sarkozy expressed shock that a boy could be attacked for wearing a skullcap, and there has been continuing debate about what Rabbi Haim Nisenbaum, of the Beth Hanna synagogue and religious school, calls “diffuse anti-Semitism.”

“We have a new problem,” he said. “It’s not anti-Semitism like before World War II. No one says, ‘Kill all the Jews’ or even ‘We’re against the Jews.’

“The problem is first social and cultural,” he said, with the resentment of poor Arabs from northern Africa and blacks from Mali and Congo who have not been integrated into the French state, aimed at better-off Jews, many also originating from northern Africa, who consider themselves integrated.

The police investigated this month’s beating of the young Jews and found no connection to anti-Semitism. Mrs. Ben Simon calls that ridiculous, but Fatma Ajimi, 22, who lives near the synagogue and was wearing a lavender head scarf, said that the police were correct — that youths insulted one another and got into a fight. “If it were really religious it would have started a long time ago,” she said.

Youssef, 33, who cuts hair in a salon on the Rue de Crimée, in the Arab sector, confirms tension between Arabs and Jews. “All the communities are separated here,” he said, speaking on condition that his last name not be used. “But it’s not a question of religion so much as territory.”

Along the Rue Tanger, the Adda’wa Mosque is being rebuilt as one of the largest in Europe, with a study center, after construction was frozen for two years. A radical cell accused of sending insurgents to Iraq through Syria was broken up three years ago by the French police and was alleged to have operated from the mosque. But Mr. Chahrine of the community center argues that most local Muslim youth are apolitical. “They don’t even know where Israel is, let alone understand their own religion,” he said. “It’s not an extreme Islam here.”

But there is anomie and restlessness and lack of opportunity. A 22-year-old woman who grew up in the large apartment blocks of the black and Arab district said, “It was quiet here until a few years ago, and now it grows,” with more guns, more drugs and more gang violence. “The police are very aggressive with us, but they solve nothing,” she said, speaking on condition of anonymity. Even 10 years ago, her mother told her to call the fire department, not the police, in an emergency because the firefighters would at least show up.

Maïa de la Baume contributed reporting.

Copyright 2008 The New York Times Company