It added that many humanitarian groups who no longer operate in Zimbabwe agree that "fundamental political and economic changes" are a prerequisite to reengagement in Zimbabwe.
The report said the US government had made known to Zimbabwean officials the importance of lifting political restrictions and curbing human rights abuses.
"To encourage greater public debate on restoring good governance in the country, the United States sponsored public events that presented economic and social analyses discrediting the government's excuses for its failed policies," the study said.
"To further strengthen pro-democracy elements, the US government continued to support the efforts of the political opposition, the media, and civil society to create and defend democratic space and to support persons who criticized the government."
Mugabe has frequently lashed out at the US and European countries, blaming them for the country's economic problems and for stoking violence.
In a press briefing on the State Department's report, Assistant Secretary of State Barry Lowenkren said the US goal in Zimbabwe was not necessarily regime change but to "give them a level playing field".
"When you have a country in which individuals are protesting peacefully and they're clubbed, one almost to death, then I think it's the responsibility not only of the United States, but all countries, …to stand up and ask how much longer are we going to sit passively by and allow this to continue?"