From Michael Ledeen at NRO's The Corner, here's a statement from Mir Hossein Mousavi's office:

Dear Mr. President,

In the name of  the Iranian people, we want you to know that when you recently made the statement "Achmadinejad or Mousavi? Two of a kind,” we consider this as a grave and deep insult, not just to Mr. Mousavi but especially against the judgment of the Iranian people, against our moral conviction and intelligence, especially those of the young generation that comprises a population of 31 million.

It is a specially grave insult for those who are now fighting for democracy and freedom, and an unwarranted gift and even praise for Mr. Khamenei, whose security forces are now killing peaceful Iranians in the streets of every major city in the country.

Your statement misled the people of the world.  It was no doubt inspired by your hope for dialogue with this regime, but you cannot possibly believe in promises from a regime that lies to its own people and then kills them when they demand the promises be kept.

By such statements, your administration and you discourage the Iranian people, who believe and trust in the values of democracy and freedom.  We are pleased to see that you have condemned the regime’s murderous violence, and we look forward to stronger support for the rightful struggle of the Iranian people against the actions of a regime that is your enemy as well as ours.

Obviously, Mr. Mousavi understands that to the extent he maintains a studied neutrality, Obama is effectively siding with the mullahs.