The Night Wolves are visiting Serbia and Bosnia's Serb-dominated Republika Srpska semi-autonomous region this week. About 20 members arrived on Tuesday.
Their stated purpose is to "research the cultural influence of the Russian empire in the Balkans".
However, many are alarmed the group has another agenda.
In 2014 the group was placed under U.S. sanctions for participating in a pro-Russian separatist insurgency in Ukraine.
Authorities are worried the Night Wolves are stoking anti-Western sentiment and pushing for a separatist movement among Serbs in the country.
Bosnian authorities declared the group a security threat and have banned entry for the Night Wolves' leader Alexander "the Surgeon" Zaldostanov.
"The tour will go on, even without me. They can't stop it," Zaldostanov told Interfax news agency.
Also called "Putin's Angels" for their close ties to Russian President Vladimir Putin, the group is expected to meet Night Wolves chapters in the region along with politicians, most notably Milorad Dodik, Republika Srpska's president, who has threatened to hold a referendum on secession for years, in violation of the Dayton peace agreement that ended the 1990s Bosnian war.
Based in Luhansk, eastern Ukraine, the Night Wolves say they are motivated by Christianity and patriotism.
"We are just the same as the military. The idea of the motorcycle club is to take back the Russian lands that were separated and Moscow links everything," one of its members said in a video from 2016.
Earlier this month Curtis Scaparrotti, head of United States European Command (EUCOM ), pinpointed the Balkans as the region he is most concerned about because of Russian influence.
'No honest intentions'
Dragan Mektic, Bosnia's minister of security, told Al Jazeera with the arrival of the Night Wolves, Republika Srpska authorities have shown "there are no honest intentions", citing reports the group plans to open an office in Banja Luka, the region's capital, to monitor the upcoming presidential and parliamentary elections in October.
"The arrival of classic motorbikers isn't controversial. But if you come with certain political messages, which in these turbulent times in Bosnia and Herzegovina could provoke certain tensions and create fear, then of course it's not good for Bosnia," Mektic said.
"Some statements, some dissident tones and hints of theirs could worsen certain tensions here in Bosnia, provoking certain reactions and counter-reactions."
Referring to the "fearmongering" led by Republika Srpska's leadership in order to sway votes, Mektic said: "There is a single goal here and that is to divide citizens in Bosnia and Herzegovina as much as possible. That way it becomes easy to manipulate them."
An estimated 500-600 Russian and Greek volunteers previously fought alongside the Bosnian Serb army in the early '90s with the aim of creating a "Greater Serbia" in Bosnia, in which more than 100,000 people were killed.
The Russian embassy in Bosnia rejected any notion that the motorcycle club presents a security threat.
"Unfortunately in this unfounded campaign, Bosnian authorities are also involved, whose main task is to strengthen security, not undermine it," the embassy said in a statement to Al Jazeera.
"We emphasise that no credible evidence has been submitted for unfounded allegations at the expense of social organisations registered in Russia."
This month Mektic - an ethnic Serb and member of Republika Srpska's opposition Serb Democratic Party - confirmed in an interview that Serb ultra-nationalists aligned with the government have been training in military camps in Russia.
He accused Republika Srpska's leadership of "fearmongering" by organising paramilitary groups and disproportionately arming the region's police to undermine the country's integrity.
This follows news in January that a militia called Serbian Honour, which reportedly trained in a Russian-funded "humanitarian centre" in Serbia, was organising a paramilitary unit to back Dodik's separatist aspirations.
The news, confirmed by Mektic, was echoed in a report published last week by the U.S.-based Foreign Policy Research Institute, titled Bosnia on the Russian Chopping Block, which details the ways Russia has been supporting "political and paramilitary actors seeking to divide Bosnia and Herzegovina".
"By supporting secessionist actors in Bosnia, Russia hopes to establish a client state in Europe, where it can damage NATO credibility and weaken the Transatlantic Alliance," the report said.
In the Balkans, the only countries that have not joined NATO yet are Macedonia, Kosovo, Serbia and Bosnia. In June 2017, Montenegro signed up.
The report highlights three groups vital to Russian interests that operate under the guise of registered NGOs - Serbian Honour, Night Wolves and Veterans of Republika Srpska.
"Several sources told us that Serb Honour members receive military training in eastern Bosnia and that there is a trainers programme led by former FSB, former Russian intelligence officials," said Professor Emir Suljagic, one of the authors of the Foreign Policy Research Institute report.
However, Dimitar Bechev, Senior Nonresident Fellow at Atlantic Council and author of the book Rival Power: Russia in SE Europe, said Russia's alleged aims of destabilising Bosnia are overplayed.
"I believe Russia, including the Kremlin, have close ties to the RS [Republika Srpska] leadership. They have been providing diplomatic cover for Dodik over the years. However, Moscow isn't actively pushing for the full-blown unravelling of Bosnia. What they benefit from is the status quo - constant tensions, the EU looking impotent, and the US hobbled," Bechev said.
"An escalation might lead to risks. I'm not sure Russia can shoulder yet another military conflict far from its borders. Their focus is on seeking a deal with the Trump administration. Right now Bosnia looks like a bargaining chip. If conflict gets worse it might turn into yet another impediment in Russia's already-strained ties with the West, plus a drain on Moscow's scarce resources."
Most worringly, the report noted, Republika Srpska has been stocking up on its weapons cache rapidly. The government has purchased more than 4,000 automatic rifles in the last two years, compared to 851 long-barrel rifles registered in 2004.
"[The new purchases] are military type weapons that are rarely, if ever necessary for any police force," Suljagic said.
"I'm very concerned. If you speak to European ambassadors in Sarajevo, they will tell you that their priority is the non-existent Turkish influence in the Western Balkans, whereas the very specific Russian activities are dismissed, which is really alarming. The EU is again gambling with peace and security in the same way as in the '90s.
"It's the same group of countries that in 1992 considered genocide against Bosnian Muslims during the war to be - officials called it - the 'very painful [but realistic] restoration of Christian Europe'.
"Right now we are alone and part of our motivation behind writing this report was to alert our allies and friends from Washington, Ankara, London that what's going on doesn't bode well for the future of the region."
By Mersiha Gadzo, Al Jazeera