MOSCOW -- As dusk fell, nine young men gathered on a leafy street in Chertanova, a bedroom community on the outskirts of Moscow. Their hair cropped short, some put on surgical masks and thick work gloves. Aleksei Khudyakov, their leader, issued final instructions like a platoon leader briefing his soldiers for a raid.
"The dorms where they live are on the other side of the building," Mr. Khudyakov, 25, explained as his cadre shuffled with anticipation.
"They" are the latest target of political and popular outrage here: unregistered immigrant workers, especially those from former Soviet republics like Uzbekistan and Tajikistan. And Mr. Khudyakov's team intended to catch them where they slept.
"We're going to go in," he told the group, half warning and half pleading with them to refrain from violence or even foul language, "but we're not going to be rude. I don't want to see aggression."
They call themselves Moscow Shield, a self-described "rights" organization that, like dozens of others here, is attracting young men and women, some out of zeal and others out of boredom, a search for purpose or a sense of belonging.
The group breaks into cramped basements and other crowded living spaces identified through anonymous tips from residents, and then tries to hold immigrants there until the police arrive. In an online tally, Moscow Shield claims to have "discovered" more than 600 illegal migrants, seven of whom have been deported, since its creation in March.
Even as Russia has cracked down on many nongovernmental organizations, especially those perceived to challenge the authority of President Vladimir V. Putin, loosely organized groups like these appear to be thriving, particularly those adhering to an increasingly conservative public agenda.
Like Cossack patrols in southern Russia or improvised neighborhood watch programs fighting drug dealers, Moscow Shield has been given unusual latitude by the police -- and at times tacit assistance -- as its members sometimes have pursued aggressive, even illegal, tactics.
The group, like other nationalist and patriotic youth organizations, is giving auxiliary support to Russia's on-again, off-again crackdown on immigrant workers, which intensified last month when the police interned about 1,500 migrants in an outdoor detention camp.
"They've found themselves a safe niche," Alexander Verkhovsky, the head of the SOVA Center for Information and Analysis, which monitors extremism in Russia, said of the anti-immigrant groups. Disenchanted with big politics, younger groups have opted for more direct action in the past two years, he added.
"In the end, it is just fun for them," he said. "To go in, push people around. They're young, after all."
Moscow Shield, the creation of Mr. Khudyakov, a six-year veteran of a pro-Kremlin youth group called Young Russia, has held more than 50 "raids" -- surprise inspections of the basements and street-level workers' quarters that house some of Moscow's estimated two million illegal migrants.
"They think that we are Nazis," said Anton Zharkov, 20, a buzz-cut, blue-eyed university student who takes part in the group's raids with his girlfriend. "But we're not there to beat them or punish them. We are there to achieve justice."
Mr. Khudyakov, a graduate of the elite Bauman Moscow State Technical University, began providing tips on illegal migrant communes to Russia's Federal Migration Service as part of Young Russia in 2009.
In 2011, he joined the Youth Anti-Narcotics Spetsnaz, a group that violently ambushed sellers of a synthetic drug called "spice." Its members often came armed with sledgehammers, to smash through front doors and disable getaway cars, and with crimson spray paint, to color the hair of their targets as others held them down.
Now, Mr. Khudyakov says he has parted ways with his past groups to work on social causes.
"Yes, we break a few locks because otherwise it is not possible to do what we do," Mr. Khudyakov said in an interview. "But we're ready to pay the fine for that."
Critics, like Mr. Verkhovsky, say they are vigilantes.
"They are acting as they believe that Russia's police should, and that more or less means that they are taking the law onto themselves," he said.
Some other movements have drawn news media attention and investigations by the police in recent weeks. Occupy Pedophilia, a movement championed by a prominent nationalist, Maksim Martsinkevich, has violently harassed and ambushed gay teenagers by luring them into meetings through VKontakte, Russia's version of Facebook.
The group, which claims it focuses on pedophiles, has spread to cities across Russia, where local affiliates carry out their own attacks, and then upload the videos to the Internet.
Mr. Martsinkevich, who goes by the nickname Hatchet, spent three years in prison for inciting ethnic hatred after he staged a mock execution of a Tajik drug trafficker and uploaded the film to YouTube.
Last month, the police announced that they had raided the homes of members of Occupy Pedophilia. As a result, Mr. Martsinkevich asked his followers to keep the violence off-camera.
By contrast, groups like Moscow Shield seem to have found common cause with the police. In certain districts, members say they have even been used as support in some large operations.
In one raid last month, five organizations -- including Moscow Shield and two others known as Light Russia and Attack -- claimed to have caught more than a hundred illegal migrants while the police supervised the operation. Video of the raid showed muscle-bound young people wrestling migrant workers in the stalls of a market.
A spokesman for the district police said its officers do not hold joint raids with activists. But organizers for several of the groups said that about 40 members of law enforcement, including local police and immigration officers, attended the raid. Photo and video reports uploaded to social networking sites showed officers and group members making arrests side by side, and the police marching detainees to buses.
"We create a perimeter; the police check documents," said Igor Mangushev, the head of Light Russia, which has been holding raids for two years and asserts that it has had more than 1,000 migrant workers deported.
In a telephone interview, Mr. Mangushev said that his group had cooperated with the police in joint raids in three city districts. Last month's operation also served as a training exercise for newer organizations, he added.
"Moscow Shield came along as sort of master class," Mr. Mangushev said. "They have a lot of young people, and they don't always work properly."
At the apartment building in Chertanova, the young men of Moscow Shield did not need to break in; the door was unlocked. The group entered an apartment with five men inside and beds for 12. A dozen pairs of slippers lay on the floor. The smell of a plov, a Central Asian rice dish, wafted through the house.
A resident who gave only his first name, Numon, and his age, 23, said that the others had locked themselves in a back room when they saw the intruders.
Mr. Khudyakov's team called the police. As two officers checked the men's documents, Yunus Z. Daminov, 24, one of a dozen men from Uzbekistan who live in the apartment and carry trash for buildings in the neighborhood, said it was not the first time that strangers had broken in. There had been other intrusions, and attacks on the street outside of the apartment.
"There were two of them, twice my size," said Mr. Daminov, a broad-chested man who sat hunched over on a bunk bed as he recalled a previous episode. "They didn't say anything. They pointed at me, and that was that. They started kicking and punching me. I lost consciousness."
He did not file a police report, and the attackers were never found, he said.
In the apartment hallway, a police officer approached Mr. Khudyakov and said that everyone living in the house, Mr. Daminov included, was registered.
"We understand what you're doing," the police officer said to Mr. Khudyakov. "Have you had any other complaints in the neighborhood?"
This article originally appeared in The New York Times.