Refat Chubarov, a Crimean Tatar leader who was banned from Russia after the annexation, told the Pryamyi television channel that Ms. Kashka had fallen ill while her home was being searched on Thursday, though that was contradicted by other reports. She died some time later in the hospital.

He described Ms. Kashka as “a legendary woman of the Crimean Tatar national movement” who had worked with the Soviet dissidents Petro G. Grigorenko and Andrei D. Sakharov to defend the rights of the displaced people. She had been targeted in an operation of Russia’s Federal Security Service, he said.

“The goal of this operation is new arrests of activists of the national movement and discrediting of the Mejlis of the Crimean Tatar people,” Mr. Chubarov said, referring to an assembly that was declared extremist by Russia in 2016. Mr. Chubarov, currently serving in the Ukrainian Parliament, is the chairman of the Mejlis.

In a statement earlier this month, Human Rights Watch accused the Russian government of intensifying the persecution of the Tartar minority in Crimea, “with the apparent goal of completely silencing dissent on the peninsula.”