You might've mixed up your analogy there, Gestapo was a German 3rd Reich thing… NKVD would be the Soviet one.
But maybe I read wrong history books.
(FYI, the NKVD killed more than 100'000 Poles in a just a few months in 1941. I haven't found a total. But they were also active in all of the CCCP. Not sure what would be an Eastern Europe specific reference here…)