The US says the violence which ravaged Sudan's Darfur region - which it views as genocide - constituted the world's worst human rights abuse in 2006.
The four-year conflict in Darfur has left more than 200,000 dead
In its annual human rights assessment, the US also flagged up a decline in government accountability in Russia and a deteriorating situation in China.
Violence in Iraq and Afghanistan was said to be hampering rights advances.
The report also looked inwards, acknowledging questions over some US anti-terror actions since 9/11.
The survey, conducted by the US state department, called what it and human rights groups consider genocide in Darfur the "most sobering reality" of last year.
"The Sudanese government and government-backed Janjaweed militia bear responsibility for the genocide in Darfur, and all parties to the conflagration committed serious abuses," it said.
These abuses, it said, included killing of civilians, the use of rape as a tool of war and systematic torture.
At least 200,000 people are estimated to have died in the four-year conflict in Darfur.
The UN last year passed a resolution imposing sanctions on Sudanese nationals accused of war crimes, but has stopped short of calling the conflict genocide.
North Korea topped the section on the world's "most systematic human rights violators", with the government said to control almost all aspects of citizens' lives.
Burma, Iran, Zimbabwe, Cuba, China, Belarus and Eritrea were also mentioned under this heading.
The secretive North Korean government came in for criticism
Russia was taken to task over "the further erosion of government accountability", the report citing restrictions on the media, police corruption and political pressure on the judiciary.
In Chechnya, serious human rights violations by both federal and Chechen security forces were also continuing, the report said.
Rights in China, meanwhile, were getting worse in some areas, with members of some ethnic, religious or political groups facing increased harassment and repression.
And ongoing conflict in new democracies such as Iraq and Afghanistan was said to be thwarting human rights advances.
In Iraq, sectarian violence and acts of terrorism "seriously undercut" progress, the report said.
The report also highlighted challenges facing NGOs and the media, saying that "a disturbing number of countries" had passed laws targeting these sectors in 2006.
But there was some good news, with human rights improvements in Liberia, Indonesia and Morocco acknowledged and praise for elections in Haiti and Ukraine.