A woman wearing a scarf depicting the Syrian opposition flag as she walks through ruins Sunday in Deir ez-Zor.
At least 200 Russian-speaking Salafi Muslims are fighting against Bashar Assad's regime in Syria, according to an expert at a state-run think tank.
Rais Suleimanov, head of the Kazan-based Volga Center for Regional and Ethno-Religious Studies, said he got this number from Russian militants themselves, who he said have "no interest in exaggerating it."
He said the militants come from CIS countries including Ukraine and from different regions of Russia, among them Tatarstan and the volatile North Caucasus, where Russian law enforcement is battling an intractable insurgency of separatist Islamist militants.
Other experts cast doubt on the reliability of the figure cited by Suleimanov, saying it was virtually impossible to verify. But they said that given Russia's staunch support of the Assad regime, it would be natural for militants opposed to the Russian government to help fight a kind of proxy war in Syria.
Factions within the Syrian rebel forces are believed to favor the creation of a Sunni Islamist state, and the vast majority of North Caucasus Muslims are also Sunni. Assad's government is largely supported by Shiite Muslims.
The presence of Russian-speaking militants in Syria could be a serious cause for concern for the Russian government, the experts said, given the likelihood that they could return to Russia battle-toughened.
The fact that some of the militants allegedly in Syria may be from outside the North Caucasus could also be a source of worry for the government, as it shows the spread of extremist Islamist ideology in Russian Muslim communities.
In July, Tatarstan's top Muslim leader, Ildus Faizov, miraculously survived three bomb blasts that destroyed his car in Kazan in the first major attack against religious leaders outside the North Caucasus. Minutes before, a former aide to Faizov was shot dead by gunmen in the Volga city.
The apparently coordinated attack, a day before the start of the holy Muslim month of Ramadan, raised fears that Islamic radicalism had spread to the more secular Muslim regions of central Russia.
According to the Kavkazchat website, a resource apparently frequented by Russian-speaking militants, fighters from "the Caucasus Emirate, Crimea, Russia, Tatarstan and several other CIS countries" do battle in Syria under the umbrella of an organization called the Kata'ib Mohadzherin.
According to Suleimanov, the combatants are led by some of the most prominent figures in the Russian radical Islamist movement, including Airat Vakhitov and Daud Khalukhayev.
In 2005, he was arrested by Tatarstan authorities in connection with the bombing of a gas pipeline in the Tatarstan town of Bugulma that year but was later released, also due to insufficient evidence.
A Facebook page apparently operated by Vakhitov, under his alias Salman Bulgarsky, contains dozens of photos and videos of militants supposedly taken in Syria, along with calls in Russian for fellow Russian-speaking Muslims to join the war against Assad.
Khalukhayev created a Chechen fighters brigade in Aleppo, Syria, and was shot dead by Syrian government forces, according to the Kavkazpress website.
In July, Chechen leader Ramzan Kadyrov said that reports about Chechens fighting in Syria were part of a campaign "to discredit Russia's position on Syria."
Alexei Malashenko, scholar-in-residence at Carnegie Moscow Center, said he doubted the reliability of information regarding Russian militant activities in Syria.
But he said that while Suleimanov's data may not be completely accurate, it highlighted the very important problem of the radicalization of Islam in Russia.
"The Russian government has not paid enough attention to how Islam is gradually changing the face of many Russian regions," he said.
On Monday, the Federal Security Service detained 10 members of the Islamic fundamentalist organization Noordzhular in St. Petersburg as part of an apparent campaign against Muslim militants.
Malashenko said that members of Noordzhular are "nice old ladies" in comparison with members of an organization like the Muslim Brotherhood, the global group that calls for the introduction of strict adherence to Sharia.
Georgy Mirsky, a research fellow at the Institute of the World Economy and International Relations, agreed that it was difficult to verify the credibility of Suleimanov's information. But he said it made sense that Russian Islamic militants would fight in Syria given that Arab militants came to Chechnya to fight against the Russian government in a separatist war there in the late 1990s and early 2000s.
Addressing the possible threat of Islamic extremism in Russia, Mirsky recalled meeting with radical Islamists in Namangan, Uzbekistan, 20 years ago. He said they told him that they would first create a Muslim state in the Fergana Valley in Uzbekistan that would subsequently absorb all of Uzbekistan, then Kazakhstan, and from there "it's a stone's throw to Tatarstan."
"It's fair to think that these ideas are absurd," Mirsky said. "But you have to remember that there are people who are willing to die for them and kill other people in the meantime."