From all reports, it was the Egyptian police, who remain staunchly loyal to Mubarak. They’d changed into plain clothes are were attacking the anti-Mubarak forces, as well as trying to cause general chaos.
This has been verified by reporters from all over the world, who are on site. Doing a Google search will bring up a lot of news stories about it, if you don’t trust American sources.
They are trying to create support for the idea that Mubarak must remain in power because only he can keep peace in Egypt. (That’s been the rationale for funding him for thirty years, after all.)
The same media told me that they were eating each other after a New Orleans Hurricane and how dangerous and violent the tea parties are.