Mr. Sulton founded a newspaper, Vatandosh (the name means “countrymen”) for Uzbek-speaking residents in Brooklyn. In an interview over kebab and plov at Lazzat restaurant in Bath Beach, he said he was warned by friends not to be too outspoken, lest he earn enemies among possible extremist sympathizers.

Such dread and censorship is one reason many immigrants came here. Uzbekistan, in Central Asia, bordered by Tajikistan, Turkmenistan, Kyrgyzstan and Kazakhstan, is predominantly Muslim. In the years after independence from the Soviet Union, in 1991, the country’s persecution of Muslim clerics prompted a wave of migration, and Brooklyn became a haven.

Of the nearly 56,000 Uzbek immigrants in the United States in 2013, according to the latest American Community Survey from the census, almost half live in New York City. About 12,000 Uzbeks live in Brooklyn, more than double the number in 2000. The population has more than tripled in the neighborhoods of Borough Park, Kensington and Midwood, as well as Homecrest and Sheepshead Bay, according to demographers at Queens College.

In Brooklyn, at least, post-Soviet immigrants from Central Asia may live near one another and share some customs, but tend to stick to their own. One sunny afternoon, a group of men were playing a serious game of cards on Ditmas Avenue. Asked if, by chance, they were from Uzbekistan, one man turned from his hand and said: “Azerbaijan. Uzbek, next block!” Then, “Wait, have some tea!”

Immigrants from Uzbekistan have been arriving in New York with help from a diversity visa lottery program, which the United States government created in 1990 to foster immigration from countries with previously low rates. The State Department issues 55,000 green cards every year through its diversity visa program and for the 2014-15 year, 4,368 were allotted to Uzbek lottery winners, the department said.

Abdurasul Hasinovich Juraboev, 24, the lead defendant accused of trying to join the Islamic State, arrived in Brooklyn in 2011 by himself and, according to a federal complaint, had a green card, a fact that stirred resentment.