KYIV -- Russian officials have blocked Crimean Tatar leaders from leaving Crimea on the eve of a major world congress scheduled in Ankara this weekend.

The chairman of the Central Election Commission of the Crimean Tatar Assembly (Qurultay), Zair Smedlyaev, told RFE/RL that he and Nariman Celal, the first deputy of the Crimean Tatars' self-governing body, the Mejlis, were handed subpoenas by the Russian investigative committee's directorate in Crimea on July 28.

According to the subpoenas, Smedlyaev and Celal must report to the investigative committee on August 1 for questioning about clashes in February 2014 that pitted Crimean Tatars and pro-Ukrainian activists against pro-Russian activists near the regional parliament.

The World Congress of Crimean Tatars is scheduled for August 1-2. Some 200 Crimean Tatar groups from several countries are expected to attend the gathering.

Smedlyaev says the subpoenas were handed to prevent his and other Crimean Tatar leaders' participation at the international event in Turkey.