Armed and masked men cordoned off the the Crimean Tatars' main assembly in the region as security officials searched it, said a member of the ethnic minority, which widely opposed Russia's annexation.
Russia wrested Crimea away from Ukraine and annexed it in March in spite of opposition from the Tatar community, who make up 300,000 of the Black Sea peninsula's 2 million people and are under pressure to align themselves with the new authorities.
"I came to work shortly after 9.30 a.m. but the building was blocked by armed people in balaclavas and uniforms," Dilyaver Akiyev, head of the secretariat of the assembly, or Mejlis, said Tuesday by phone.
"They are not letting anyone in or out, they are assisted by regular police and the FSB [Federal Security Service] is carrying out searches inside," he said from Crimea's provincial capital Simferopol.
Footage from the site showed several armed men masked by black balaclavas guarding the site.
The FSB declined to comment.
Crimean Tatars are deeply distrustful of Moscow after mass deportation of their kin to Central Asia in 1944 under Soviet leader Josef Stalin.
The community leadership ordered a boycott of a popular vote in Crimea that showed a majority of residents supported joining Russia. Tatars called for autonomy and shunned regional elections after the annexation.
At least two of the Crimean Tatars' senior leaders are now living outside the region and accuse Russia of not allowing them back in.
"The policy of mounting pressure on us, on the Mejlis and the community, continues and is growing in force," Akiyev said. "That is to force us to conform with the new authorities, especially now after the elections.
"But we are not breaking any laws, there are no grounds for any searches," he added.
The Council of Europe's human rights commissioner, Nils Muiznieks, says pressure has increased on Tatars since the annexation, including raids on their businesses and schools.
Russian President Vladimir Putin in April signed a treaty rehabilitating them along with other ethnic minorities who suffered under Stalin.
The mix of pressure and promises to respect their rights has left Crimean Tatars split over whether to resist or deal with Russia.
Kiev and the West introduced sanctions against Russia over Crimea and then expanded them as the pro-Russian separatist unrest spread to eastern Ukraine.
Unlike in Crimea, which was seized by Russian troops largely without bloodshed, the conflict in eastern Ukraine has killed more than 3,000 people, according to the United Nations.