We know they do it. They know we know they do it. But they still cannot acknowledge it. It is just how things work.
When the Wikileaks leak happened, there was an article (or comment on HN) about how seemingly obvious things are still classified. Say that US govt. knows about the crimes some dictator is committing against his own people. The locals in that country know it (and experience it). The world, including US citizens know it or can very easily find out, yet the fact that US government knows is classified.
The reason is because an official acknowledgement would also demand some sort of official denouncement or some other similar action in order to maintain a certain propaganda-ready image (universal support for human rights, democracy & freedom promotions etc etc)