"Several thousand people from CSTO countries are fighting in Syria on the side of the militants," CSTO Secretary General Nikolay Bordyuzha said to Interfax-AVN.
He could not voice a particular figure. "It could be two or ten thousand. Once there was said 10, then suddenly -two. This figure is constantly changing, someone dies, someone comes back," CSTO Secretary General said.
"In general, we are talking about 10,000. There are precise data on countries. We know how much are from Russia, who are from Kyrgyzstan and Tajikistan. Special services maintain these lists, identifying those who leave," he said.
The Secretary General noted that the countries of the Collective Security Treaty Organization track militants who return from the zone of armed conflict in Syria.
"We have introduced a system of monitoring the flow of migrants from the zone of armed conflict to track the tendency in whole," he said.
"Particular attention is paid to people from five countries: Afghanistan, Syria, Yemen, Libya, Iraq," Nikolay Bordyuzha said.
According to him, the secret services fix the facts of return of militants involved in the Syrian conflict to CSTO countries.
The CSTO consists of Armenia, Belarus, Kazakhstan, Kyrgyzstan, Russia and Tajikistan.