Beijing - China's authorities are moving against the signatories of a public appeal asking for more freedom and democracy in the country, human rights activists said Thursday.

Several prominent activists who signed the document, called Charter 08, have been detained by the authorities, Human Rights Watch said in a statement released in Hong Kong.

At least 10 other people have been questioned by police, the statement said.

"The drafters and signatories of an historic public appeal for human rights and democracy in China are facing unprecedented retaliation by the government," Human Rights watch added.

Liu Xiaobo, 52, head of China's Pen Club of independent writers as well as one of the charter's 303 signatories, remains in police custody following his arrest on Monday.

Police in Beijing remained silent on the charges levelled against the prominent dissident. "He was taken away without any explanation," his wife Liu Xia told Deutsche Presse-Agentur dpa on Thursday. "I am worried about him."

Efforts to get an explanation for his arrest remained fruitless, she added.

The fact that China arrested dissidents on the day of the 60th anniversary of the Universal Declaration of Human Rights, was particularly telling, activists said.

"To commemorate human rights day by harassing signatories of a petition and arresting leading dissidents suggests that the Chinese government remains hostile to fundamental rights including expression and association," said Sophie Richardson, Asia advocacy director at Human Rights Watch.

She called for their immediate release.

"By affixing their names to the charter the signatories knew they would face official retribution," Richardson said. "Their courage must be recognized, and their actions defended."

German Foreign Minister Frank-Walter Steinmeier, commenting on Liu's arrest on Wednesday, said Germany must not stay silent on human rights violations. "Even against China, especially today," he said. (dpa)