The British-based rights body said government security, intelligence and police services continue to abuse human rights despite last year's landmark elections, designed to end years of war and chaos in the vast, unruly central African state.
"Far from protecting the people of the DRC, the state security services remain agents of torture and death," it said.
Amnesty said confused and conflicting lines of command and a culture of human rights violations had contributed to widespread abuse surrounding the elections, in which Kabila defeated opposition leader Jean-Pierre Bemba, a former rebel leader.
Coquette Nsinga, a 25-year-old student and a member of Bemba's political party, was led from her cell at night and raped by five police officers last November, two weeks after she and her mother were arrested following the final poll, it said.
In particular, Amnesty said security forces had abused civilians and even members of other services suspected of supporting Bemba after Bemba loyalists fought Kabila troops in two days of bloodshed in the capital Kinshasa last March in which up to 600 people were killed.
Amnesty cited accounts of government forces executing dozens of people detained at the city's Tshatshi military camp.
It quoted a civilian identified as Cyrille K, 32, who was arrested by Kabila's Republican Guard at his Kinshasa apartment and taken to the camp where, after being beaten, he and three fellow detainees were forced to strap heavy car wheel hubs to their backs and promised some "peanuts" -- slang for bullets.
Cyrille never saw the other three after they were marched off towards the Congo river, where he suspects the wheel hubs were intended to weigh down their bodies.
He was spared, only to endure further torture.
"The next day, he was taken out, tied up, forced to his knees and beaten again with planks of wood. Then, on orders from an officer, a soldier forced his penis into his mouth. He was led to the camp latrines and made to clean them on his knees," Amnesty said.
The report said Congolese police, paid around $10 a month, were responsible for an increasing number of human rights violations in recent months, including many rapes.
Amnesty said failure to complete the reform of the array of armed forces left by decades of chaos and a five-year war, which had once been seen as essential to last year's elections, had left security units under "confused or conflicting chains of command" with some answerable to individual politicians.
Congolese army units are still fighting dissident militias in eastern Congo who have refused to integrate into the army.
"In the east, where the conflict has never conclusively ended, grave human rights violations continue to be committed by government forces as well as by Congolese and foreign armed political groups," Amnesty said.
In a separate report, the Swiss branch of medical aid agency Medecins Sans Frontieres (MSF) said on Wednesday that despite a reduction in ethnic violence in Congo's eastern district of Ituri, rape continued unabated -- mostly by armed rebel or government troops.