"In recent weeks, supporters of President Robert Mugabe’s ZANU-PF party in Harare have targeted perceived supporters of the MDC formation led by Prime Minister Morgan Tsvangirai with violence, with the tacit approval of the police," Amnesty said in a statement.
"It is an open secret that ZANU-PF supporters who use violence against members of the public or their perceived political opponents are beyond the reach of the law," added the rights group’s Africa director, Erwin van der Borght.
"Police have continued to selectively apply the law — turning a blind eye to violations by ZANU-PF supporters while restricting the work of human rights organisations and the activities of other political parties."
Mugabe’s ZANU-PF has traded accusations in recent days with the MDC, its partner in an uneasy power-sharing government, over which party is responsible for the new outburst of violence.
Amnesty’s statement came days after hordes of youths, some of them wearing ZANU-PF t-shirts, attacked traders at a popular mall in Harare.
The youths claimed they were protesting the slow implementation of equity regulations to give locals majority shares in foreign-owned firms.
The rights group said its delegates had also seen ZANU-PF supporters beat members of the public in the presence of riot police during a protest at Harare’s Town House.
The statement said a high school student was beaten by the mob for taking a picture, while a young woman wearing an MDC T-shirt was beaten and stripped.
Amnesty said it had also received reports of MDC supporters being attacked and evicted from their homes in the Harare suburb of Mbare.
"These events are just the tip of the iceberg. Thousands of people in rural areas live in fear of violence amid talk that the country might hold another election in 2011," van der Borght said.
"Concrete reforms of the security sector are urgently needed before the next elections are held."
Mugabe and Tsvangirai formed the power-sharing government two years ago to mend an economy ravaged by hyperinflation and avoid a descent into civil war in the wake of a bloody presidential run-off election.
Mugabe is pushing for fresh elections this year despite a deadlock over a new constitution that was supposed to pave the way for the next polls.