"We are bracing ourselves for a difficult time in Zimbabwe. Every time there are elections there is violence," Crisis in Zimbabwe Coalition spokesman Dewa Muvhinga told journalists.
"Those we expect to uphold the rule of law are not independent, they are partisan to Mugabe," he said.
He said Mugabe used military and police to arrest a cabinet minister and lawmakers, to intimidate civil society and to jail journalists.
Prime Minister Morgan Tsvangirai, Mugabe’s partner in a shaky unity government, earlier this month called for the country to hold polls under a roadmap by the Southern African Development Community (SADC), the regional bloc that brokered the power-sharing deal.
Mugabe and Tsvangirai formed the unity government two years ago in a bid to end political violence and to ensure basic rights, such as freedom of speech and assembly.
But this month Tsvangirai’s Energy Minister Elton Mangoma was charged with abuse of office over a fuel purchase, while the Supreme Court nullified the election of his party’s chairman as parliamentary speaker.
Lawmakers aligned with Tsvangirai, independent journalists and political activists have been jailed since December, when Mugabe hinted at polls for 2011. An upsurge in political violence in rural areas has also been reported.
A SADC security summit will meet next week to discuss the situation in Zimbabwe.
"The current political environment is not conducive for a free, fair and credible elections," Muvhinga said.
"Human rights in Zimbabwe is rapidly deteriorating, Mugabe continues to use the state machinery to violate people’s rights."
Tiseke Kasambala, a researcher for Human Rights Watch, said the SADC should be involved in Zimbabwe to avoid conflicts like in Libya and Ivory Coast.