A congressionally mandated annual report by the US State Department reviewed the rights record of nearly 200 countries across the globe in 2005.
As well as Iran and China, the report singled out North Korea, Myanmar, Zimbabwe, Cuba and Belarus, which it said allegedly subjected their citizens "to a wholesale deprivation of their basic rights”.
Referring to those seven, it said "countries in which power is concentrated in the hands of unaccountable rulers tend to be the world's most systematic human rights violators."
"These states range from closed, totalitarian systems that subject their citizens to a wholesale deprivation of their basic rights to authoritarian systems in which the exercise of basic rights is severely restricted," it said.
On the more positive side, the report lauded what it called "marked overall improvement" in human rights, democracy, and the rule of law in the Balkans in Europe and the Great Lakes region of Central Africa.
Poor record
Referring to Iran, the State Department said the "already poor record on human rights and democracy worsened" in the Islamic republic last year under hardline President Mahmoud Ahmadinejad.
It warned that together with Syria, they posed "threats" to neighbouring countries and the international community.
"We must call countries to account when they retreat from their human rights commitments," Secretary of State Condoleezza Rice said in unveiling the report.
The report also cited Iran's "deprivation of basic rights to its own people, its interference in Iraq, its support for Hezbollah, Hamas and other terrorist organisations and its refusal to engage constructively on these issues."
It accused President Ahmadinejad of condoning deterioration in prison conditions for hundreds of political prisoners, restrictions on press freedom and a rollback of social and political freedoms.
The human rights record of China, the report said, "remained poor," accusing the government of "serious abuses".
"Those who publicly advocated against Chinese government policies or views or protested against government authority faced harassment, detention and imprisonment by government and security authorities," it said.
The report also highlighted "repression" of minority groups and of unregistered religious groups, citing, in particular, cases of Uighurs and Tibetans fighting for separation or greater autonomy and the Falun Gong spiritual movement.
The report did not elaborate on rights abuses in Iraq, where the bombing of a Shiite shrine in February triggered the worst sectarian violence since the March 2003 US-led invasion and left hundreds dead, mainly Sunnis.
It admitted however that "elements of sectarian militias and security forces frequently acted independently of government authority" in Iraq.
The United States is an aggressive global rights watchdog but in recent years seems to have lost its moral authority on the issue after charges of abuse of prisoners in Iraq and the secretive detention and coercive techniques used against prisoners elsewhere.
Human Rights Watch, another rights watchdog, had said the broad US-led "war on terror" has also led to charges of torture and inhumane treatment of detainees and fuelling erosion of human rights across the globe.
This had hampered Washington's ability to pressure other states into respecting international rights laws, it said.
Iraq torture claims
Rights group Amnesty International charged this week that tens of thousands of people had been held "arbitrarily" since the US-led invasion.
Most of those held were neither charged nor faced trial and had no basic right to challenge their detention, Amnesty said.
Detainees in Iraq are being tortured with electric shocks and beatings using plastic cables despite US promises to prevent such abuse after the Abu Ghraib scandal, a report by Amnesty International said.
It said many of the reported abuses occurred at facilities controlled by Iraqi authorities.
"Many cases of torture and ill-treatment of detainees held in facilities controlled by the Iraqi authorities have been reported since the handover of power in June 2004," the report said.
A US military spokesman for detention operations said in response that all detainees are treated according to international conventions and Iraqi law.
Amnesty said interviews with former detainees, relatives of current detainees and lawyers involved in detainees' cases in Iraq showed that prisoner mistreatment has not ceased since the mistreatment revealed at Abu Ghraib prison by US forces three years ago.
"Since Abu Ghraib, the multinational force -- and the United
States in particular -- promised they would put safeguards in place," Amnesty spokeswoman Nicole Choueiry said. "But the (lack of) legal safeguards are still an obstacle to detainees getting and enjoying their human rights."
In the Abu Ghraib case, photographs from 2003 showed Iraqi inmates being abused, triggering worldwide outrage that led to military trials and prison sentences for several lower-ranking American soldiers.
In the new allegations, former detainees claimed they were beaten with plastic cables, given electric shocks and made to stand in a flooded room as an electrical current was passed through the water, Amnesty said.
The US military said all detainees are given a form explaining the reasons for their imprisonment and their files are reviewed every 90 to 120 days.
In February, new images of naked prisoners, some bloodied and lying on the floor, were broadcast by SBS television.
The images were taken about the same time as the earlier photos three years ago that triggered the worldwide scandal.