If the SVR is Russia’s CIA or MI6 then Zaslon is comparable to the CIA’s Global Response Staff (GRS), the CIA’s high-security detail, or the even more secretive E-Squadron. The US Army’s Task Force Orange AKA intelligence support activity (ISA) conducted similar functions, supporting CIA intelligence officers in hostile environments. Incorrectly, some sources claim that Zaslon is the equivalent of the CIA Special Activities Center. Of course, culture and political systems impact doctrine of these organistations so it remains difficult to compare.

https://inmoscowsshadows.wordpress.com/2013/05/11/the-mystery-that-is-zaslon/