The U.S. State Department Tuesday again called on China to immediately release dissident figure Liu Xiaobo, a writer detained a year ago after joining others in signing a pro-democracy declaration. In an address on human rights policy Monday, Secretary of State Hillary Clinton vowed to press human rights concerns with world powers like China and Russia despite other U.S. interests with them.

The State Department has raised the case of Liu Xiaobo for a second straight day despite a warning from China that it considers outside expressions of concern meddling in its internal affairs and judicial sovereignty.

Liu, a former university professor, has spent the last year in prison for co-authoring a pro-democracy petition known as Charter 08, which calls for major political reform in China including democratic change and respect for human rights.

In a statement volunteered to reporters at a press briefing, Assistant Secretary of State for Public Affairs P.J. Crowley noted that Liu was formally indicted on subversion charges on December 10 - International Human Rights Day - and that the United States is deeply concerned about the development.

"According to all publicly-available evidence, the basis of his prosecution is that he has signed and supported Charter '08, which calls for respect for human rights, universal human rights, and democratic reform," he said. "Mr. Liu has already spent a year in detention while authorities carried out an investigation of his case."

"We call on the government of China to release him immediately and to respect the rights of all Chinese citizens to peacefully express their political views and desires for universally-recognized fundamental freedoms," he added.

Crowley said the comments on the Liu case are fully consistent with Obama administration human rights policy as outlined by Secretary Clinton in a Washington policy address Monday.

Clinton said the administration is pursuing an agile and pragmatic policy that will hold all nations accountable for meeting international human rights standards, the United States included.

She said in some cases public criticism of countries is the most effective way to influence rights case while with others like major powers Russia and China it might require tough negotiations behind closed doors.

On China, Clinton urged protection of minority rights in Tibet and the largely Muslim Xingjiang region and said the United States believes strongly that peaceful advocates for reform, like the Charter 08 signatories, should not be prosecuted.

Clinton came under criticism from U.S. human rights groups for comments just before a visit to China in February for suggesting that rights advocacy with China cannot interfere with global issues on the agenda such as the global economy and climate change.

But she was more assertive on rights issues at a high-level U.S. Chinese dialogue in July.

A spokeswoman for Amnesty International welcomed the Secretary's speech Monday but said closed-door U.S. contacts with China and Russia on human rights should be complemented by public pressure.

A Chinese Foreign Ministry spokeswoman said Tuesday U.S. and European Union criticism of China on the Liu Xiaobo case is unacceptable. She said the rights of Chinese citizens are guaranteed by the law and that outsiders have no right to interfere with Chinese judicial bodies.