Russia foils IS attack on security services, ministry employees
"Members of the group planned to detonate an explosive close to an administrative building belonging to security services, followed by an armed attack against interior ministry employees" in regional capital Makhachkala, the FSB said in a statement.
As well as arresting four "members of the international IS terrorist group", investigators found "firearms and bladed weapons, a large amount of ammunition and an explosive device", it added, along with mobile phones containing "exchanges with organisers located abroad".
On December 17, police killed two attackers targeting security forces in Russia's neighbouring republic of Chechnya.
Six people were also killed during an October "counter-terrorism" operation in Chechnyan capital Grozny, including two members of the security forces.
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Russia's territories in the Caucasus were ravaged by two wars between federal troops and Chechen separatists in the 1990s and 2000s.
Increasingly Islamist in character, the insurgency spread to other republics in the region and declared allegiance to IS in 2015.
While the jihadist group's influence remains limited, occasional attacks against the authorities persist in Chechnya, Dagestan and neighbouring Ingushetia.
Agencies contributed to this report.