The United Nations High Commissioner for Human Rights, Louise Arbour, is asking China for more information on its policy of capital punishment.
China's communist leaders have traditionally been reluctant to discuss their capital punishment policy, and do not disclose how many people Chinese courts execute every year.
Human rights advocates believe China to have among the highest number of executions in the world, and note that the authorities hand down death sentences for crimes of varying severity - from murder to tax evasion. But the activists have never been able to come up with a reliable number.
On Friday at the end of her five-day visit here, U.N. human rights chief Louise Arbour called on the Chinese government to provide more information. She indicated she was especially concerned that ethnic minorities and mentally ill convicts might be receiving inordinate numbers of death sentences.
"We know from worldwide experience that very often when you go beyond the numbers, you uncover patterns of sometimes indirect discrimination," said Louise Arbour.
There was no immediate comment from Chinese officials on whether they would comply with Ms. Arbour's request for information.
During her stay, the U.N. official met with Chinese officials including ministers, the head of the Supreme Court, and selected activist groups. Security at venues where she appeared was tight, as the authorities worked to keep her away from people trying to hand her petitions.
On Wednesday, Ms. Arbour and Chinese Assistant Foreign Minister Shen Guofang signed an agreement by which the United Nations and China will coordinate efforts to reform China's legal system. The aim is to allow China to ratify the U.N. International Covenant on Civil and Political Rights.
In the course of her visit, she also raised the cases of several jailed dissidents, including journalists and activists.
The United States has repeatedly called on China to improve its poor human rights record, citing what it says are numerous and serious abuses against members of religious, political and social groups that the Communist Party sees as threats to its authority.