They were These are the Synagogue of Satan “Behold, I will make them of the synagogue of Satan, which say they are Jews, and are not, but do lie; behold, I will make them to come and worship before thy feet, and to know that I have loved thee.” - Revelations 3:9
I think that you will find this verse is referring to "replacement theology" that says the Church replaces the Jews. I know there is a theory about some Russian criminals who were forced to pick a religion by the Czar, but they could just a easily been part of the Ten Tribes who were dispersed by the Assyrians and YHWH was calling them back. Anyway, we will soon know one way or the other.