US Secretary of State Hillary Clinton has criticised China for what she calls its worsening human rights record.
She expressed concern over reports of Chinese intellectuals and activists being "arbitrarily detained" in recent weeks - including the arrest of prominent artist Ai Weiwei on Sunday.
She was speaking as the State Department released its annual report on human rights around the world.
The survey assesses the state of human rights in 194 countries.
The State Department also highlighted serious violations in Iran, Iraq, Burma, North Korea, the Ivory Coast, Zimbabwe, Ukraine, Russia and Belarus.
'Courage and determination'
Unveiling the report in Washington on Friday, Mrs Clinton said the US was deeply concerned by recent reports of arrests - including Mr Ai's.
"Such detention is contrary to the rule of law and we urge China to release all of those who have been detained for exercising their internationally recognised right to free expression and to respect the fundamental freedoms and human rights of all of the citizens of China," she said.
As it covers 2010, the report does not focus on the revolutions that have swept across the Middle East and North Africa this year, toppling long-time authoritarian leaders in Tunisia and Egypt as well as sparking uprisings in Bahrain, Libya, Yemen and elsewhere.
But Mrs Clinton said the US was "particularly inspired by the courage and determination of the activists in the Middle East and North Africa and in other repressive societies who have demanded peaceful democratic change and respect for their universal human rights", AFP reported.
In the introduction to its 2010 Country Reports on Human Rights Report , the state department said: "At this moment, we cannot predict the outcome of these changes and we will not know the lasting impacts for years to come.
"The United States will continue to monitor the situations in these countries closely, knowing that the transition to democracy is not automatic and will take time and careful attention," it added.