BEIJING (AP) — Hundreds of Chinese activists issued an unusually open call Tuesday for greater freedoms and an end to China's one-party rule, and advocates said police detained two of the signatories before the statement was even issued.

The online statement — called the '08 Charter and signed by a group of more than 300 lawyers, writers, scholars and artists — represents a new public call for change in a country where criticizing the ruling Communist Party often brings swift punishment.

The statement proposed 19 measures to improve rights in China, including promoting an independent legal system, calling for freedom of association, and ending the monopoly of one-party rule. It was issued to coincide with Wednesday's 60th anniversary of the U.N. General Assembly's adoption of the Universal Declaration of Human Rights, a document that inspired many later human rights treaties.

China signed the U.N. treaty but has not ratified it, meaning it is not bound by it.

"This charter promotes the same ideas and values that the Universal Declaration of Human Rights asserts, such as freedom of the press, freedom of association, independent justice, freedom of religion and environmental protection," said lawyer Mo Shaoping, who signed the statement.

"It has nothing that goes against China's constitution," he said.

However, one activist, Zhang Zhuhua, said police showed up at his house Monday night and detained him for questioning, holding him for 12 hours before releasing him Tuesday morning.

"They said I was involved in drafting the '08 Charter and warned me not to do it anymore. They searched my home and took my computer, books and bank cards," Zhang said.

Also detained Monday was Liu Xiaobo, an outspoken writer and political critic who had previously been jailed for his role in the 1989 Tiananmen Square protests, Zhang said.

Liu, 53, is a former Beijing Normal University professor who spent 20 months in jail for joining the 1989 student-led protests in Tiananmen Square, which ended when the government called in the military — killing hundreds, perhaps thousands.

It was unclear Tuesday if Liu had also been released. His cell phone was turned off, and his home number rang busy.

Chinese police did not respond to questions on the detentions made by phone and fax.

Nicholas Bequelin of New York-based Human Rights Watch said the '08 Charter was significant because it brings many diverse, prominent figures in China under a common agenda to promote human rights.

He said the charter gives concrete proposals and focuses on the legal protection of human rights rather than blaming the Communist Party. Still, he expected police to investigate those who signed it.

China does not want domestic opposition to its human rights record because it harms efforts to defend its record internationally, he said.

"The Chinese government really insists that human rights concerns are an external agenda imposed by Western countries and Western governments, but this gives the lie to this thesis," he said.

In an interview with the official Xinhua News Agency, Wang Chen, the director of the State Council Information Office, said China has seen great improvements in human rights over 30 years of social reform, but acknowledged there were "still many problems and difficulties in the development of human rights."

He said such problems include social inequalities, weaknesses in the country's political structure and a lack of awareness by all levels of government.

However, Wang also chided critics of China's human rights record, saying in particular that the U.S. State Department's criticism was "unfounded" and that the U.N. charter does not allow the international body to intervene in "matters that are essentially within the domestic jurisdiction of any state."