Mikhail Zvinchuk, who is also a former Russian defence ministry official, was detained with others including his wife in the Adriatic resort of Risan on charges of spreading "Russian influence," Pobjeda newspaper reported citing sources.
Rybar - one of the most popular blogs on Russia's war in Ukraine, with more than 1.5 million subscribers - posted a message saying Zvinchuk and the others had been in the country legally and were planning to film at a monastery there.
"Since there were no violations of local legislation, we expect all detainees to be released," Rybar said.
The Russian embassy in Podgorica said it had demanded clarification on the reasons for the arrests.
The blog is part of a network of sites and media feeds covering a wide range of Russian activities.
The United Kingdom imposed sanctions on 10 individuals linked to Rybar in July, saying the media company was resourced by the Russian state and "responsible for spreading false narratives about Ukraine and interfering in European elections, including in Moldova and Armenia".
Russia has regularly denied accusations of misinformation and sabotage campaigns.
Montenegro has long had fraught relations with Russia.
In 2016, authorities there accused Russia of plotting with a group of Serbian ultranationalists to stage a coup, a charge the Kremlin denied.
Ties soured further when the small Adriatic republic joined the NATO military alliance in 2017.
Montenegro, a candidate for membership in the European Union, enforced sanctions against Russia over the war in Ukraine in 2022, banned Russian state media and expelled Russian diplomats for spying.
In a retaliatory move, Russia declared it an enemy state.
Montenegro Prime Minister Milojko Spajic posted a message on X confirming Zvinchuk's detention and saying it had followed warnings that the country would face attempts to destabilise it and hybrid warfare - acts that fall short of direct military conflict.
"There are serious indications that require every lead to be carefully examined and every connection to be viewed in a broader context," he wrote.
"The message after today's successful operation, in which the head of the Rybar information network was detained, is clear ... Montenegro is protecting its interests, and no one will jeopardise our European future," he added.
Montenegrin police and the ANB state security agency said four Russian citizens they identified only by initials "were uncovered and processed".
"It was determined that these persons cannot continue their stay in Montenegro ... (and) it was decided to expel them from Montenegro for reasons of national and internal security of the state," the statement read.
A police source confirmed the four were Zvinchuk and the other Russians.
In October 2024, the US State Department offered a reward of up to $US10 million ($A14 million) for information leading to the identification of 19 individuals involved in managing Rybar-led social media channels, saying they had promoted Russia's political interests in the United States ahead of the 2024 presidential elections.
"Rybar has sought to ... promote social division, stoke partisan and racial discord and encourage hate and violence in the United States," the State Department's Rewards for Justice program said.
After Friday's arrest, Dmitry Medvedev, the deputy chairman of Russia's Security Council, said on Friday that Russia may need to "top up" its prisoner exchange fund with European and US citizens to free its own citizens being held in Europe.
"It's a mistake, of course, for our people to be travelling around European countries. Even if they have good intentions and important goals. Potentially, all (and I emphasise – all) Russians are being hunted down," Medvedev said on Telegram.
Russia's military bloggers have acted as cheerleaders for the war in Ukraine while sometimes criticising Russian military commanders for their handling of it.
Rybar maintains close ties to the Russian military and provides detailed daily frontline updates.
This and other military blogs play a significant role for both warring sides, as they operate with more freedom than official military public relations channels.
with DPA
