Russian President Vladimir Putin is scrambling to reassure his nation that everything is being done to prevent fresh terrorist attacks, as dozens of people were detained in a police sweep on Tuesday of Volgograd city, the target of two separate bombings.
The attacks on a railway station on Sunday and a trolley bus a day later left 33 dead and scores more injured.
Mr Putin now chairs daily emergency meetings of Interior Ministry officials and has ordered Mr Alexander Bortnikov, head of Russia's domestic intelligence agency, to fly to Volgograd to supervise anti-terrorist measures.
But, coming a mere six weeks before his country hosts the Winter Olympics, the terrorist crisis is a huge embarrassment for Mr Putin, who came to power on an anti-terrorism ticket. The attacks are also an unwelcome public reminder of the degree of lawlessness which prevails in Russia's rebellious, Muslim-populated Caucasus region.
No group has claimed responsibility for the attacks and Russian officials remain unsure why Volgograd has been targeted. It is likely though that hitting this city of one million inhabitants resonates with ordinary Russians, for it is synonymous with national bravery: It was where the Soviet Union scored its first major triumph against the invading forces of Nazi Germany in World II.
But the purpose of the attacks is obvious: to inflict maximum casualties in the lead-up to the Winter Olympics, on which Mr Putin has already lavished US$40 billion (S$51 billion), four times what the British spent on the 2012 London Olympics.
The attacks bear all the hallmarks of a loose alliance of Islamist terrorist organisations grouped around the self-proclaimed "Caucasus Emirate", which seeks independence for Muslim communities in Russia's southern provinces adjacent to the Black Sea, a struggle which has already generated two major wars in Chechnya, at a cost of roughly 100,000 lives.
In purely military terms, the Russian authorities have prevailed, killing all the top insurgent commanders. Russia also poured huge resources into reconstruction: The pockmarked buildings of Grozny, Chechnya's capital, were replaced with housing estates and one of Europe's largest mosques.
Still, none of this helped integrate local Muslims into Russian society; the revolt now infects other Caucasus ethnic groups, and is increasingly assuming an Islamic rather than just a separatist character. Dagestan, the autonomous republic next to Chechnya, is now a hotbed of international terrorism: Tamerlan Tsarnaev, a suspected bomber of last year's Boston Marathon, hails from its capital Makhachkala.