The attackers have shown no mercy, putting mines on roads, setting off car or truck bombs and sending suicide bombers, sometimes young women, into Russian subways, buses or train stations.
The carnage they've been wreaking is instant and the numbers are surprisingly high: 659 killed and 490 wounded in 182 "terrorist attacks" in Russia last year alone, according to the U.S. State Department.
Now Russian security forces on the lookout for three female suicide bombers amid fears one of them is in Sochi, where the Winter Olympic Games begin in less than three weeks. That hunt comes just days after those same forces went on combat alert after a series of unexplained killings involving booby-trapped bombs in an area north of the Caucasus — it was like a second shoe falling after the twin bombings in Volgograd just before New Year's.
So just who are the kingpins behind the Islamist insurgency that has been fomenting for many years in the predominantly Muslim North Caucasus region, not so very far from Sochi?
And how big a threat are they?
Somewhat surprisingly, security analysts aren't quite sure because the nature and direction of Russia's terrorist problem are all over the map.
"What the Russian government is facing now is less a classic terrorist campaign like the IRA, or even like the Chechen separatists in the 1990s and early 2000s, and more like a diffuse expression of rage at the authorities, which is to some extent orchestrated and managed by concrete figures such as Doku Umarov," says Matthew Light, a professor at the Centre for European, Russian and Eurasian Studies at the University of Toronto.
Umarov's name often comes up in connection with the North Caucasus insurgency. He has been reported dead several times, most recently last week, although that couldn't be confirmed. But in a video statement last summer, the Chechen rebel who now is said to head the umbrella militant group Caucasus Emirate urged his followers to "do their utmost to derail" the Sochi Games.
The Caucasus Emirate, a Sufi nationalist organization formed by Umarov in 2007, "aims to have an independent Caucuses Emirate ruled under Shariah and to abet a global jihad," according to the U.S.-based Terrorism Research and Analysis Consortium.
TRAC claims a number of regional militant groups exist under the CE umbrella including:
- the Yarmuk Jamaat, active in the republic of Kabardino-Balkaria, which turned to ambush-style tactics in 2010;
- the Ingush Jamaat, active in many areas within Ingushetia and linked mainly to deaths of police officers, military personnel and officials;
- the Dagestani Shariah Jamaat, the most prominent Islamist militant group in Dagestan, which uses tactics ranging from assassinations and drive-by shootings to kidnappings and improvised explosive devices
- Riyad us-Saliheyn Martyrs' Brigade, which aims to form an independent Islamic state in Chechnya and uses suicide bombings.
Limited survival prospects
Efforts by Russian security forces to wipe out local or regional leaders with the Caucasus Emirate mean its leadership is always in flux, says TRAC, which currently lists seven men within the CE leadership, including Umarov.
"In Dagestan, the 'republic' leader hardly ever survives for more than one year at a time," says TRAC. "During January 2013, in Chechnya, the Gakaev brothers, famous and well-respected warlords among the Chechen guerillas, were killed."
The Canadian government has labelled the Caucasus Emirate a "terrorist" group under the Criminal Code.
Steven Blaney, the federal minster of public safety and emergency preparedness, announced the listing of that group and Boku Harum of Nigeria late last month.
"Listing terrorist entities facilitates the prosecution of perpetrators and supporters of terrorism, as well as countering terrorist financing," Blaney said in a release.
Fluctuating leadership contributes to the difficulty of knowing exactly who may be orchestrating attacks throughout the region.
After the fact, individuals may be identified as suicide bombers, but assessing to what extent they acted on their own or were directed is difficult. Also, some militants might decide to undertake attacks on their own to garner attention and move up the ranks, security experts say.
All the local sectors within the Caucuses Emirate are decentralized and free to experiment, says Gordon Hahn, a senior associate with the Centre for Strategic and International Studies in Washington, D.C.
Umarov may be the driving force within the organization, Hahn says, but local groups "don't need to get Umarov's permission to carry out a suicide bombing.
"They do their own planning, they do their own recruiting."
As much as Umarov has developed a high profile, Light, for one, isn't sure he would call him the "biggest threat" to security around the Sochi Games. But he wouldn't rule him out, either.
On whose orders?
"He is, as far as we can tell, the senior figure in all the jihadi movements in the North Caucuses and certainly claims to be their leader, although that's different from saying he's actually orchestrating or ordering all these attacks," Light said in an interview from Tbilisi, Georgia, where he is doing research on police reforms and other security issues.
"It seems likely. I think he probably is. I just don't know whether we have the proof of that."
Hahn also question whether Umarov is the sole motivator behind the recent attacks in Russia. He says most of the suicide bombings since 2010 have occurred in Dagestan or were organized by the Dagestani mujahedeen.
"Forget about Chechnya," he said, in an interview from California. "This is largely driven in Dagestan by intensely religious emirs who buy in entirely to the ideology of al-Qaeda."
This week, the Vilayat Dagestan, one of the units of the Caucasus Emirate, claimed responsibility for the suicide bombings last month and threatened to strike the Games.
Hahn doesn’t, however, rule Umarov out. He sees him as one of the two most likely threats to the Olympics, particularly through the Riyad us-Saliheyn Martyrs' Brigade that Umarov revived in 2008.
"He seems to run that directly though another guy," says Hahn.
The other most likely threat Hahn sees comes from the Dagestani network within the CE and its version of a suicide martyrs' brigade that was organized in 2010 and specializes in recruiting ethnic Russian suicide bombers.
The earliest suicide bombing originating with that group, Hahn says, was in February 2011, when a couple blew themselves up in the Dagestani village of Gubden. And authorities have said they believe one of the two Vogograd bombings last month was by an ethnic Russian who converted to Islam.
A 'sea of insecurity'
Part of the problem for Russian security forces right now, Light suggests, is paradoxically the result of earlier success in the region during two periods of fierce fighting and brutal repression in the 1990s.
"The Russians successfully destroyed the Chechen secular nationalist movement that was the source of some earlier terrorist attacks."
At the same time, the situation in most North Caucasus republics is now dire. There's high unemployment. Local governments are repressive and corrupt. Some young people are angry and blame the Russian state.
"As in other parts of the world, including to some extent Canada and the U.S., some of those young people will see radical Islam as a source of inspiration or something that helps them make sense of the problems they face in … their lives," says Light.
In the end, he suggests, the security problems surrounding the Sochi Olympics can be traced to those unresolved political and social problems in the North Caucasus.
"It's difficult to create an island of temporary security in a sea of insecurity."