Russian authorities have detained at least 23 Crimean Tatars on suspicion of being members of a banned Islamic group this week.

The Federal Security Service (FSB) raided the homes of 25 Crimean Tatars in Simferopol, detaining 20 on Wednesday and three more the next day. The predominantly Muslim ethnic minority has largely opposed Russia’s 2014 annexation of Crimea from Ukraine and has seen its local self-governing body banned as an extremist organization.