Reports of killings and torture by the Iraqi government and its agents increased in 2005, a US report says.
The state department's annual report says Iraqi police abuses included threats, intimidation and beatings, as well as the use of electric shocks.
China, North Korea, Burma, Iran, Zimbabwe, Cuba and Belarus are named as among the worst human rights offenders.
The report does not mention the US treatment of detainees in Iraq, Afghanistan or Guantanamo Bay, Cuba.
Washington has come under strong international criticism for its treatment of prisoners and has faced calls from the UN to shut down the Guantanamo detention camp.
The report acknowledges that the US's "own journey toward liberty and justice for all has been long and difficult, and it is far from complete".
The report highlights abuses by Iraq's security forces, describing "a climate of extreme violence in which people were killed for political and other reasons".
The worst abuses against prisoners were carried out by police but the military was also a violator, the report says.
In particular, the document mentions "suspension by the arms or legs, as well as the reported use of electric drills and cords".
It adds: "The ongoing insurgency, coupled with sectarian and criminal violence, seriously affected the government's human rights performance."
The report also highlights severe rights abuses in a number of other countries:
China: "there was a trend towards increased harassment, detention and imprisonment by government and security authorities of those perceived as threatening"
Iran: summary executions, different forms of torture and violence by militias with ties to the government continued
Burma: extrajudicial killings, rape, torture and beatings of prisoners and detainees continued
North Korea: "extrajudicial killings, disappearances, and arbitrary detention, including many political prisoners" continued
Israel and the occupied (Palestinian) territories: the Israeli government generally respected the human rights of its citizens, but security forces committed serious abuses against Palestinian detainees; also Palestinian attacks against Israeli civilians and the military continued
Russia: a trend toward "erosion of the accountability of government leaders to the people", including corruption, selective law enforcement and pressure on the judiciary
Sudan: there was evidence of continuing genocide in the western region of Darfur blamed on the government and allied militia; also serious abuses by anti-government rebels
The report also singles out Zimbabwe, Cuba and Belarus - along with China, Iran, North Korea and Burma - as countries that allegedly subjected their citizens "to a wholesale deprivation of their basic rights".
Introducing the report, US Secretary of State Condoleezza Rice said she hoped it would "encourage governments, organisations, the media and publics to address human rights problems".
The report has been published annually by the state department since 1977.