World rights group Amnesty International says Zimbabwe's police and military have mounted an "alarming clampdown" on basic freedoms ahead of crucial national elections on July 31.

Noel Kututwa, an Amnesty director for Africa, said Friday the organization documented clear partisan support for President Robert Mugabe by top security commanders along with "systematic raids and arbitrary arrests" targeting human rights and democracy activists.

He called on security forces to respect and protect fundamental freedoms.

Mugabe proclaimed the July 31 poll despite calls by regional mediators for a delay to allow the completion of democratic reforms and a clean-up of chaotic voters' lists.

Prime Minister Morgan Tsvangirai has been in a shaky coalition with Mugabe since the last violent and disputed polls in 2008.