Last Tuesday, just 24 hours after suicide bombers killed 39 people on the Moscow metro, a pair of explosions claimed 12 more lives in Dagestan, a republic near Chechnya, in Russia's troubled south. Wednesday saw two further fatalities, as another bomb went off in the same region.
It was a bloody week in Russia and there is apprehension that terrorist violence, linked to Islamist separatists in the Caucasus, could escalate yet further.
Life has remained cheap in Chechnya and Dagestan, but the carnage on Moscow's metro demonstrated that insurgents are willing and able to wreak havoc right at the centre of Russian power.
The two female bombers who carried out the attacks are thought to belong to a group known as the 'Black Widows', which came to prominence during the Moscow theatre siege in 2002.
Under the tutelage of Chechen terror chief Doku Umarov, it is feared that 30 new members have been trained to commit further atrocities.
Although the title suggests that this suicide squadron comprises women whose husbands have been killed by Russian authorities in Chechnya, often they are simply teenage girls, who have been sold by their families, kidnapped or drugged. It is a tragic indictment of the region's lawlessness.
The perpetrators of last week's attack targeted two of central Moscow's busiest metro stations, striking during rush-hour.
Neither target was chosen at random. Lubyanka sits a short distance from an enormous building which once housed the KGB. It is now home to Russia's latest security apparatus, the FSB.
Experts suspect that the Park Kultury bomb was destined for a station further down the line, adjacent to the Russian Interior Ministry. Russia is no stranger to terrorist attacks and neither is its capital. In December, a bomb planted by Umarov's group killed 26 people travelling on the busy rail link between Moscow and St Petersburg. The Moscow underground has also been targeted before, with deadly consequences.
The connection between each attack is the apparent involvement of Chechen rebels. Russia fought two wars to pacify the Caucasian Republic, and while an uneasy peace has been attained, Islamic militancy has spread to neighbouring Dagestan and Ingushetia.
Umarov, whose group claimed responsibility for the Moscow attacks, professes to be fighting for an independent, Islamic 'Caucasian Emirate' which would span the entire region. Militant Islam contributes to a volatile mix of separatism and tribal rivalries in the Caucasus.
Chechnya itself is experiencing relative stability under Ramzan Kadyrov, a former rebel, whom former Russian president and current prime minister, Vladimir Putin, tasked with maintaining order. Kadyrov's methods have proved brutally effective.
The republic's capital, Grozny, which was left a charred ruin after the second Chechen War, has been rebuilt with Russian money, and a degree of normality has returned to its streets. Part of the legacy which Putin passed on to his successor, Dmitry Medvedev, was supposed to be a pacified Caucasus. Many Russians are prepared to tolerate low level insurgency in the country's remote south, as long as it is contained, but a bloody reminder that the terrorists' reach extends deep into European Russia puts pressure on the Kremlin.
The reaction from Putin and his government was swift and predictable. The Prime Minister, who once threatened to "waste" terrorists "in the outdoor toilet", has vowed to "scrape them out of the sewers". His Interior Minister, Nikolai Patrushev, alluded to possible involvement by Georgia, which has, in the past, provided shelter for Chechen rebels. The truth is that Russia and the west face a common enemy. However, for Russia, it is an enemy within, and the threat it poses is complicated by a history of misgovernment and nationalist separatism.
While the Kremlin relies on a policy of divide and rule among tribes and criminal gangs, the region will remain volatile and a terrorist threat will persist.
Owen Polley is a commentator and blogger