Amnesty International on Thursday accused Angolan security forces of extrajudicial killings and the use of excessive force in suppressing dissent against the government of veteran ruler Jose Eduardo Dos Santos.
The rights watchdog released a report cataloguing over 20 protests that have been put down with disproportionate force over a two-year period.
Amnesty said the Angolan authorities action against protestors is tantamount to an "effective ban" on all anti-government demonstrations.
Most have been about a lack of electricity and water supplies; forced housing evictions and mysterious disappearances of demonstrators in the oil-rich country.
It cited the cases of two men -- Silva Alves Kamulingue and Isaias Sebastiao Cassule -- who went missing after organising demonstrations against the Luanda administration in March 2012.
It emerged later that the pair had been killed by "state agents", said Amnesty.
Another political activist, Manuel de Carvalho Ganga, was shot and killed by a presidential security guard a year ago after he was caught posting flyers near Dos Santos` palace.
"We are seeing a state that has turned against its own people, a government that cannot take criticism from its own citizens," said Deprose Muchena, Amnesty International`s regional director for southern Africa.
"The genuine cries of its people are met with unlawful arrests, extrajudicial killings and forced disappearances," he added.
The London-based group said Angolan police have also carried out arbitrary arrests and demonstrators have faced "politically-motivated charges and unfair trials".
Those protesters fortunate enough not to have been killed have been punched, kicked or beaten with anything from truncheons to gun butts and metal cables.
The human rights watchdog said as the member of the UN, Angola has a responsiblity to implement international human rights standards relating to policing.
The government has been trying to polish its image of late, lobbying hard for a non-permanent spot on the United Nations Security Council and taking part in multinational peacekeeping missions.
Amnesty called on Dos Santos, who has been in power for 35 years, to rein in his security forces and "to immediately end the use of excessive force" on demonstrators.