Did the Iranian government try to silence the Internet?

It has been argued that the Iranian government tried to silence Iranians active on the Internet by blocking access access to sites such as Facebook, which were being used by the supporters of Mir Hussein Moosavi to protest against the results of June 12 presidential elections.

It appears that there is some truth to it.  Iran-based computers searched for Facebook on Google the most between June 12 and 14.  From June 15 onwards, there has been a steady decline in the interest in the Facebook in Iran. One of the reasons in the drop cited by many media hawks is that the Iranian government was using filters to block access to the Facebook site. The graph below presents the dramatic decline in the internet traffic to Facebook from Iran.

The same fate was met by Twitter (see the graph below). The peak traffic was observed between June 12-June 14. The sudden increase in Twitter’s popularity around June 12 and the precipitous decline soon afterwards suggests that the elections increased the interest in Twitter, which was used by the Mousavi’s supporters to organize protests, and the sudden decline in the internet traffic is probably a result of the government restrictions.

Also note that there has been a significant increase (2500%) in the searches for Mousavi (table below), whereas only a 450% increase in searches for Admedinajad.