A new 47-page report accuses Mugabe’s Zanu-PF party of using Zimbabwe’s police and judicial system against the opposition and civil society despite a unity accord signed in September.
The New York-based body estimates that 163 people have been killed in political violence since the country’s disputed March elections, which saw Mugabe lose his majority in Parliament for the first time since independence.
"Zanu-PF’s institutions of repression remain intact, and there has been no change in their abusive conduct and attitude," said Africa director Georgette Gagnon in a statement.
"The regional leaders in SADC need to get tough on the party leader, Robert Mugabe, or ask the United Nations to intervene," she added.
South Africa will host an emergency summit of the Southern African Development Community (SADC) on Sunday, when heads of state from the 15 members will try to resolve a deadlock over the sharing of key cabinet posts between Mugabe and opposition leader Morgan Tsvangirai.
Gagnon said it was time for the regional bloc to put pressure on Zanu-PF.
"It mistakenly trusted former South African president Thabo Mbeki’s quiet diplomacy and his belief that Mugabe would restore the rule of law and respect human rights," Gagnon said.
Zimbabwe’s unity accord brokered by Mbeki is teetering on the verge of collapse over a protracted dispute on which party will control the most powerful ministries, especially home affairs which oversees the police.