YAROSLAVL, September 20 (RIA Novosti) – Some 300 to 400 Russians are fighting in the Syrian civil war as soldiers of fortune, a senior official in Russia’s Federal Security Service (FSB) told reporters on Friday.

However, as those soldiers return home, it will pose a “great danger” to Russian security, FSB first deputy director Sergei Smirnov said after a board meeting of the Shanghai Cooperation Organization’s anti-terrorism department.

Recruiting mercenaries is a real practice, Smirnov said, and preventing this kind of activity isn’t mentioned in Russian law. “We still need to work on that,” he added.

Smirnov's estimate was significantly higher than one made in May by FSB head Alexander Bortnikov, who claimed that a total of about 200 mercenaries from Russia, Europe and Central Asia were fighting in the civil war.

Smirnov said Friday that the SCO board meeting did not directly discuss the mercenary issue, but that Russian officials had privately talked about it with other member state representatives and found that they were also concerned.

The SCO, a Eurasian political, economic and military cooperative founded in Shanghai in 2001, includes China, Russia and the Central Asian states of Kazakhstan, Kyrgyzstan, Tajikistan and Uzbekistan.

Last year, the Syrian government presented the United Nations Security Council with lists of hundreds of foreign nationals who had been killed fighting against government forces in Syria. The lists included mercenaries from Arab countries, Europe, and Russia’s North Caucasus region, including Chechnya.