BRATISLAVA, Slovakia >> The People’s Party-Our Slovakia, after months of stirring up fears about foreigners and Muslim migrants, decided to take action: This spring, the group’s leader proudly stood in front of the main railway station in Zvolen, Slovakia, and announced that a new group of volunteers would begin patrolling passenger trains to keep the “decent citizens” of Slovakia safe from criminals and minorities.

Never mind that vanishingly few of the hundreds of thousands of migrants who have reached Europe over the last year ever set foot in the Central European nation, or that only 10 people last year became crime victims on a Slovakian train system patrolled by 600 railway police officers.

The xenophobic Slovakian group has been one of a wave of such extremist organizations across Central and Eastern Europe that have seized on last year’s influx of migrants through Europe to advance their agenda and build popular support. In some cases, the vigilante groups have taken to patrolling borders, streets and other public places to defend against what they portray as a menacing incursion of asylum seekers — many of them Muslims from Afghanistan, Iraq, Syria and other poor, war-torn nations.

“The original cultures of Europe are threatened by some idiots from the desert,” said Marian Magat, the leader of Vzdor Kysuce, another far-right group in Slovakia, which has actually seen few migrants pass through its borders and fewer seek to settle.

In Hungary, which saw nearly 400,000 people registered by police as entering the country illegally last year en route to Germany and other more welcoming destinations, Istvan Matyas Vass, a retired artist and former lawmaker has, since July, led a group called the Hunyadi Border-Guard Unit.

The group was named for John Hunyadi, a Hungarian military figure who won a decisive battle in Belgrade against the Ottomans in the 15th century. Vass and his more than 300 colleagues keep up a steady presence on social media, agitating about what they see as the threat from migration.

In Bulgaria, Petar Nizamov said he was proud of creating an informal group called Civil Squads for the Protection of Women and Faith, which a few months ago began hunting for migrants along the country’s borders, pushing them back into neighboring Turkey.

“Those who come to Europe now are not refugees,” Nizamov said, dressed in a long-sleeve T-shirt with the image of King Simeon the Great, who ruled Bulgaria during the late ninth and early 10th centuries. Their goal, he said, is “to spread Islam” across Europe.

The groups remain relatively small, as focused on stirring up political support and media attention as on confronting migrants, and not all of them are actively patrolling. In Hungary, Vass posted a call last year to the Hunyadi Border-Guard Unit “to be prepared to step up for your own defense.” But authorities later dropped an investigation after it became clear that the group had done nothing but prepare to take action.

Not only are there few migrants coming through Slovakia at the moment, but the government, like those of most countries in the region, is strongly resisting pressure from Western Europe to accept asylum seekers for resettlement.

Nonetheless, People’s Party-Our Slovakia, led by Marian Kotleba, is patrolling trains, so far without having to save anyone from a migrant attack. And Vzdor Kysuce is organizing and training paramilitary groups that it says will patrol the streets if migrants ever do appear in Slovakia. Magat, the party’s leader, calls the 20 people who have signed up as paramilitaries “sleeping soldiers” who have been trained to “protect the white majority” just as “people in Germany took their guns and started solving problems themselves in 1930s.”

Despite the small number of active participants, the emergence of the groups has authorities in some countries worried.

“Whenever someone’s trying to replace the state’s function in some way, it creates a dangerous precedent,” says Tomas Nociar, an expert on extremism from Comenius University in Bratislava.

And the citizens groups have been more active in Bulgaria, whose border with Turkey has been an alternate route into Europe for migrants from Afghanistan, Iraq and Syria unable or unwilling to make the voyage by sea to Greece.

Nizamov has been under house arrest since mid-April and an investigation of his activities is underway. He was detained shortly after posting a video on social media showing the apprehension of three Afghan migrants, their hands tied behind their backs. The migrants told police that the vigilantes, carrying knives and a gun, urged them to go back to Turkey.

While Nizamov is the only one who has been detained by Bulgarian authorities for a citizens arrest of migrants, his group is not alone in patrolling the Turkish border.

In April, a group of volunteers known as the Organization for the Protection of Bulgarian Citizens caught 23 Afghans and handed them over to police. The group, which organizes charity and sports events, began its patrols last year.

“We’re trying to help the state, as they don’t have enough people to properly guard the border,” said Georgi Bratanov, 29, a bartender and regular participant in the patrols.

In February, Dinko Valev, also 29, a spare parts trader, became a national celebrity after a television station broadcast a report calling him a “superhero” for catching a group of Syrian refugees, including women and a child.

At first, Bulgarian authorities turned a blind eye to the vigilante patrols and even encouraged their activities. But later, after international outrage over Nizamov’s activities, the government condemned the groups’ actions.

“Any lawbreaking or inhumane treatment” will be prosecuted, Prime Minister Boyko Borisov said, adding that his government had taken all necessary steps to secure the country’s border.

Daniel Milo, the coordinator of counterextremism policies in the Slovakian Interior Ministry, said self-styled citizens patrols present risks to themselves and the public.

“It can end up badly,” he said. “These people are not ready, nor equipped, to deal with any problematic situations.”

Websites and social media pages for Kotleba’s party depict a Slovakia awash in danger from criminals and “Gypsy extremists,” protected by patrols of tough-looking men in green shirts, decorated with the party’s logo.

Until these right-wing patrols do anything illegal, they cannot be banned, said Lubomir Abel, vice president of the Slovakian police force.

“People who used to fight us in the streets are now sitting in the parliament, wearing white shirts,” Abel said of People’s Party-Our Slovakia, which won 14 of the 150 seats in Slovakian parliament in March elections, propelled by supporters weary of the country’s inefficiency and corruption scandals.

Likewise, in Hungary, where few refugees have actually settled, the far right is waging a campaign built on ethnic, religious and racial enmity, including encouraging supporters to be vigilant against what they portray as threats to their safety and way of life — even though the flow of refugees through the country has all but stopped this year.

“Europe is Christian, they are Muslims,” Vass said in a telephone interview, speaking of the asylum seekers who poured through the country last year. “It’s a financed and organized wave by Zionist Jews to destroy Europe. The EU has a suicidal policy in accepting them.”

Peter Kreko, an analyst at Political Capital, a Budapest-based research organization, said groups like the Hunyadi Border-Guard Unit attracted only limited popular support in part because the Hungarian government under Prime Minister Viktor Orban has taken such a strong anti-immigrant position, leaving little political space for the extreme far right.

The government’s own “hard line towards migrants made it hard for those groups to find any air,” he said.