Putin wonders about Islamist terror in Russia - Why an IS strike would not be surprising. The current terrorist attack on Krokus City Hall is not the first Islamist attack that Russia has suffered from.
During the second Chechen war, Chechen fighters carried out assassinations and assassinations on Russian soil. These include several suicide bombings at the Tajikistan's embassy in Moscow. The Tajik diaspora in Moscow has even called on its citizens to stay at home for safety reasons. There is also a crunch between Russia and NATO.