* 20 anti-corruption activists detained in recent weeks
* Six more activists to be tried on Thursday and Friday
* Three activists awaiting sentences (Adds comment from U.S. State Department, paragraphs 16-18)
By Sui-Lee Wee
BEIJING, Jan 22 (Reuters) - Prominent Chinese rights advocate Xu Zhiyong went on trial on Wednesday in the country's most high-profile dissident case in years, but his lawyer said he refused to offer any defence and called the court unjust.
Outside the courtroom, Xu's supporters chanted slogans and raised banners in his support. Police pushed away the crowd and at least three protesters were taken away to a police van.
The government has waged a 10-month drive against Xu's "New Citizens' Movement", which advocates working within the system to press for change, including urging officials to disclose their assets.
The campaign against the movement exposes the ambivalence in Beijing's bid to root out corruption, even as the authorities claim greater transparency.
Xu, 40, is charged with "gathering a crowd to disturb public order", punishable by up to five years in prison. His prosecution will almost certainly spark fresh criticism from Western governments over Beijing's crackdown on dissent.
Speaking to reporters by telephone at the end of the trial, which, as is common in China, lasted a single day, Xu's lawyer Zhang Qingfang said prosecutors demanded a heavy punishment.
Xu, he added, maintained his silence throughout.
"At the end, he wanted to express freedom, justice and love in his speech, but because this content was not allowed by the courthouse and the court eventually interrupted him, he didn't say it," Zhang said.
Zhang had earlier said both he and Xu would maintain silence during the closed-door proceedings because they did not believe the court would grant a fair trial.
Zhang said that he was frustrated that the court only allowed him to produce two witnesses.
Five witnesses that he had requested testify in court have been put under police guard and been prevented from moving around freely. One of them, he said, has been taken to a motel.
"Our maintaining silence does not mean we will not express our views. But we believe this court is not worth expressing our views," Zhang said.
China has detained at least 20 activists involved in pressing for asset disclosure, though not all are from the New Citizens' Movement.
Six will stand trial in Beijing and the southern city of Guangzhou on Thursday and Friday. Three went on trial in December and face more than 10 years in prison if convicted.
Xu's trial China's highest-profile dissident proceeding since 2009, when Nobel Peace Prize Laureate Liu Xiaobo was put on trial for subversion after he helped organise the "Charter 08" petition urging the overthrow of one-party rule. Liu was jailed for 11 years.
U.S. State Department spokeswoman Marie Harf expressed concern about Xu's trial.
"We are concerned that he is being prosecuted as retribution, I think, for his public campaign to expose corruption and for the peaceful expression of his views," she told a regular news briefing in Washington.
"This is the latest in a pattern, quite frankly, of arrests and detention of public interest lawyers, internet activists, journalists, religious leaders and others who are challenging official policies and actions in China. ... We obviously call on Chinese authorities to release him and other political prisoners immediately."
Despite the increased security presence near the courthouse, close to two dozen Xu supporters turned up at the start of the trial, joining many reporters and photographers. But police pushed them away and closed off the road outside the courthouse, saying the crowd did not have permission to gather.
Three supporters were hauled away.
Hu Jia, a prominent dissident, said state security officers told him and five other activists not to leave their homes.
About 10 to 15 supporters unfurled a banner that read: "Citizens request officials to publicly disclose assets."
"Down with corrupt officials", "Xu Zhiyong is not guilty" and "Free Xu Zhiyong," they chanted.
Diplomats who tried to attend the trial were not allowed to enter the courtroom.
Daniel Delk, second secretary for the political section at the U.S. embassy, said China should release Xu and other dissidents immediately.
"The United States is deeply concerned that Chinese authorities are prosecuting prominent Chinese legal scholar and rights advocate Xu Zhiyong as retribution for his public campaign to expose official corruption and for the peaceful expression of his views," he said in a statement.
Chinese Foreign Ministry spokesman Qin Gang said Xu was suspected of crimes and was being tried "in accordance with the law".
Through his online essays and Twitter account, Xu had criticised the government's efforts at fighting corruption and prescribed democracy and the rule of law as the solution. "When more than 90 percent of the officials are corrupt, who will counter who? The social movement of asset disclosure is an effort for gradual change to the system," he wrote.
The Chinese leadership is nervous about Xu's writings, said Chen Min, a writer and friend of Xu's.
"The Communist Party does not accept pressure, the party does not accept challenges," Chen said. "Anything that the party can't control, independent and non-governmental forces - no matter how gentle the force - it has to combat."
Xu taught law at a Beijing university and ran in a local election. He became prominent over a drive to abolish "custody and repatriation" powers, a form of arbitrary detention used by local governments to sweep homeless and other undesirables from the streets. The government scrapped the system in 2003.
Xu has also campaigned for the rights of children from rural areas to be educated in cities where many live with their migrant worker parents. (Additional reporting by Maxim Duncan and Michael Martina in Beijing, Venus Wu in Hong Kong and David Brunnstrom in Washington; Editing by Raju Gopalakrishnan)