The Russian-imposed authorities in Crimea said that security forces were conducting an operation targeting alleged members of Hizb ut-Tahrir, an Islamic group that is banned in Russia.
Zaur Smirnov, the chairman of Crimea's State Committee for Interethnic Issues, said on January 26 that a "special operation" was being conducted in the city of Bakhchisaray.
He did not provide any details.
At least five Crimean Tatars were arrested in October on suspicion of being Hizb ut-Tahrir members.
Their lawyer, Emil Kuberdinov, was detained and questioned in the Crimean capital, Simferopol, on January 26 on suspicion of "spreading extremist materials."
His colleague Edem Semedlyayev said police then searched Kuberdinov's office and confiscated his computer. A court in Simferopol is expected to decide on Kuberdinov's possible pretrial detention.
On January 25, another lawyer, Nikolai Polozov, who is defending prominent Crimean Tatar activist Ilmi Umerov, was forcibly detained and questioned at the Federal Security Service (FSB) office in Simferopol.
Earlier in September, a court in southern Russia sentenced four Crimean Tatars to lengthy prison terms after finding them guilty of being members of Hizb ut-Tahrir.
Russia has been heavily criticized by international rights groups and Western governments for its treatment of Crimea's indigenous Turkic-speaking, mainly Muslim people since Russia seized control of the Ukrainian region in March 2014.
Arrests, disappearances, and killings of Crimean Tatars have been reported.
With reporting by RIA Novosti and TASS