That so-called 'warning' needs to be investigated.
It's highly highly highly doubtful that State Department was 'warning' the Russian Government. They were issuing a standard warning to Americans about traveling, gathering in groups, etc., which they issue several times a year.
The UK-Government is claiming the same thing. That is too thin to be credible, as well.
This isn't going to end well for the arrestees. I suspect it's already ending for some of them... bloody, on camera, on their knees. I wish we could do that to the violent criminal illegals here.