KYIV -- Russian investigators have summoned Crimean Tatar leaders ahead of a major world congress scheduled for Ankara this weekend in a move that has sparked concern that the authorities are trying to pressure the group.

The chairman of the Central Election Commission of the Crimean Tatar Assembly (Qurultay), Zair Smedlyaev, wrote on Facebook that he and Nariman Celal, the first deputy of the Crimean Tatars' self-governing body, the Mejlis, were summoned for questioning by the Russian investigative committee on July 28.

Smedlyaev suggested the questioning might be related to clashes in February 2014 that pitted Crimean Tatars and pro-Ukrainian activists against pro-Russian activists near the regional parliament.

Russian special forces wrested Crimea from Ukraine in the months ahead of its unrecognized annexation of the peninsula in March 2014, a move that has left Tatars and critics of the move vulnerable to abuses under Russian control.

Several Crimean Tatar activists, including the deputy chairman of the Mejlis, Ahtem Ciygoz, were arrested earlier this year and charged with organizing "mass disorder" in connection with the violence outside the regional legislature.

Armed men in unmarked uniforms -- later acknowledged to be led by Russian forces -- seized the parliament building the following day.

A UN resolution subsequently asserted Crimea's continued status as part of Ukraine.

Smedlyaev said this week's questioning might be an attempt to prevent Crimean Tatar leaders and activists from taking part in the World Congress of Crimean Tatars, slated to be held in the Turkish capital on August 1-2.

The Ankara congress is expected to attract some 200 Crimean Tatar groups from several countries.

Meanwhile, the leader of the pro-Russian Crimean Tatar organization Qirim (Crimea), Remzi Ilyasov, who is also deputy speaker of Crimea's Moscow-backed parliament, has publicly condemned the idea of holding the world congress in Ankara. Ilyasov has called on Turkish President Recep Tayyip Erdogan to boycott the gathering.

Activists say Crimean Tatars have faced discrimination, pressure, and abuse over their opposition to Russia's land grab.

Several Crimean Tatars have turned up dead since the annexation, and more Crimean Tatar activists have been arrested. The veteran leader of Crimean Tatars Mustafa Dzhemilev and Mejlis Chairman Refat Chubarov have been barred from entering Crimea by the peninsula's Russian-installed leaders.

In April, Crimea's Moscow-backed authorities shut down the only Crimean Tatar television channel and its affiliated media outlets.

Most Crimean Tatars appeared to oppose Russia's annexation of Crimea from Ukraine, while others, like Ilyasov, accepted it and have cooperated with Russian officials.

With reporting by the Crimean Desk of RFE/RL's Ukrainian Service