The report singled out regional powerhouse South Africa for particular criticism, saying that former president Thabo Mbeki had strayed from the ideals that guided the struggle against apartheid.
"Under president Thabo Mbeki, rather than join a global movement to apply pressure on the Zimbabwean government to stop its repression, Pretoria refused to speak out," it said.
"As a result, the South African government was seen as backing a repressive leader rather than his suffering victims," it added.
The report noted that Mbeki had brokered a power-sharing deal between Zimbabwe President Robert Mugabe and opposition leader Morgan Tsvangirai, but said the pact quickly deadlocked over disputes on how to form a joint cabinet.
"Zimbabwe’s political situation remains precarious, and the future looks bleak if the political leadership does not end abuses," it said.
The African Union and the 15-nation Southern African Development Community (SADC) have also failed to take strong action on Zimbabwe, even amid spiralling political violence, worsening food shortages and a deadly cholera epidemic, the report said.
"The role of SADC and the AU remains crucial in ensuring a peaceful return to the rule of law and respect for human rights, but the ongoing situation is a blot of the credibility of their commitment to an effective regional solution," it added.