On March 30, Russian authorities arrested a large cell of people apparently recruiting for the Islamic State terrorist group. Russian media hints at a Turkish connection.
Evidence of Turkish-Islamic State complicity grows from financing them through oil purchases, to supplying weapons.
Russian media does not expressly say that the Erdogan regime is behind this recruiting cell, but given all the hard evidence of Turkish support for the Islamic State, it doesn't seem unrealistic.
Considering the Russian attacks on oil tanker convoys from the Islamic State to Turkey (convoys which Turkey cannot admit exist) then recruiting within Russia seems not unrealistic as part of Turkish retaliation.