That requires you to be in the city. The USSR's oppressed minorities (and Russia's oppressed minorities today) were not in the main cities, but in peripheral areas.
Which did not stop a couple nasty attacks such as Dubrovka Theater to be carried out.
I gather that there is plenty of Muslims of Central Asian and Caucasian origin in Moscow.
Furthermore, there are some fairly major cities in Muslim majority areas in Russia today (Kazan is probably the largest) and even more so in the Soviet Union.
However, in Soviet times post-Stalin, there appears to have been very little if any specifically Muslim disaffection. The CARs were essentially thrown out of the USSR, for instance, where the elites and most inhabitants would have been happy to remain within it (unlike, say, Georgia and the Baltics). Not great recruiting ground within the Soviet Union for Islamist terrorism (indeed, most former Soviet areas are still generally not that great recruiting grounds for radical Islamists, with the notable, though very conspicuous, exception of Chechniya).