AlertsUSA initially opted to not report on this incident because of an inability to gain reliable details. 

Russian law enforcement now reports the blast was caused by a homemade explosive device.

AlertsUSA subscribers are reminded that the Islamic State has repeatedly called for attacks in the West over the end-of-year holidays, as well as regularly threatens Russia over actions in Syria.

It should be noted that one of the largest pools of foreign fighters in Syria and Iraq come from the Russian Northern Caucasus regions of Chechnya, Dagestan, and Ingushetia.

Additional alerts will be issued as events events warrant.