"I believe there is no greater crime against humanity than genocide. I feel strongly that every member of the world community has a moral and ethical responsibility to act to prevent such crimes," he said.
Spielberg said he hoped all sovereign nations "will work creatively to coexist with great peace and lasting prosperity and that they will treat their citizens with dignity and respect."
Ai dismissed concerns about repercussions from expressing his views.
"It is not opposition to the state, but rather in fighting for individualism and freedom of expression, freedom of human rights and justice ... If you read newspapers today you see the problems created by this structure and by the effort to maintain power. It is against everything that human society should be fighting for," he said.