Russia's domestic security agency has detained six people in Crimea accused of involvement in an extremist organisation.
The move has been described by one of the suspects' lawyer as part of Moscow's crackdown on the Crimean Tatars.
Emil Kurbedinov, a lawyer for one of the six detainees, said police also rounded up nine other Crimean Tatars who protested against the detentions in the Crimean town of Bakhchisarai.
The Federal Security Service or FSB, the main KGB successor agency, said it has stopped the activities of a local cell of Hizb-ut-Tahrir, a radical Islamist group which Russia and several other ex-Soviet nations banned as a "terrorist" organisation.
The FSB said in a statement carried by Russian news agencies that it has opened a criminal probe against six people suspected of involvement in the group.
Mr Kurbedinov, a lawyer for Suleiman Asanov, whom the FSB accused of organising the cell, described the charges as "absurd".
He said all six detainees were local Crimean Tatar activists who opposed Russia's 2014 annexation of Ukraine's Crimea.
Russia has faced criticism for infringing on the ethnic group's rights since the annexation.
"It's yet another attempt to intimidate people with 'terrorism' and 'extremism' labels," Mr Kurbedinov said by phone from Bakhchisarai.
Mr Kurbedinov said nine other Crimean Tatars who were protesting against the detentions were taken into custody for holding an unsanctioned demonstration and were set to face court hearings on Thursday.
Zair Smedlyayev, who heads an association of Crimean Tatars, also said the move was part of a continuing crackdown on the ethnic group.
On Monday, Turkish president Recep Tayyip Erdogan, who was visiting the Ukrainian capital Kiev, said Turkey was monitoring the situation of Crimean Tatars and thanked Ukraine for defending their rights.