BEIJING -- Five years after his detention, the United States is calling for the release of Chinese Nobel Peace Prize winner Liu Xiaobo and an end to his wife's undeclared house arrest.

Washington remains deeply concerned about the couple's treatment, along with that of other jailed government critics, Secretary of State John Kerry said.

"We strongly urge Chinese authorities to release Liu Xiaobo, to end (wife) Liu Xia's house arrest, and to guarantee to Liu Xiaobo and his family members all internationally recognized human rights protections and freedoms," Kerry said in a statement issued Monday in Washington.

"As the United States builds a constructive relationship with China, U.S. leaders will continue to raise concerns related to respect for the rule of law, human rights, religious freedom, and democratic principles with their Chinese counterparts," Kerry said.

Beijing has rejected Washington's appeals as interference in its domestic affairs, and while it says Liu Xiaobo was duly convicted of subversion, it has refused to offer any legal basis for the house arrest of Liu Xia, who friends say has grown despondent at being virtually confined to her apartment for the past three years.

Kerry also raised concerns about the detention of the activist legal scholar Xu Zhiyong, who founded the New Citizens Movement, a loose network of activists who have gathered for political discussions over dinner and small street rallies.

Beijing police have recommended that city prosecutors indict Xu for allegedly organizing street demonstrations, Xu's lawyer Zhang Qingfang said.

Xu has yet to be charged for any crime, but comments Tuesday by China's Foreign Ministry spokesman indicate his conviction is likely a foregone conclusion.

The spokesman, Hong Lei, said that both Liu Xiaobo and Xu Zhiyong had violated China's laws. "They deserve to be punished by law," Hong said. "I need to emphasize that only the 1.3 billion Chinese people are best qualified to pass judgment over China's human rights condition."

Detained on Dec. 8, 2008, Liu Xiaobo was convicted of subversion in 2009 and sentenced to 11 years in prison for penning an appeal for democracy. He was awarded the peace prize in 2010. Deeply embarrassed, China's government angrily denounced the award and suspended much of its economic and diplomatic contact with Norway, where the prize is awarded.

Kerry's statement underscored a desire by the U.S. to be seen as active on Chinese human rights in the face of critics who say the issue is being downgraded because of Washington's desire for strong trade ties and Chinese support on knotty diplomatic issues such as the conflict in Syria and Iran's nuclear programs.

Hong noted that "China and the U.S. are working to build a great-power relationship."

"We hope that the U.S. can give priority to the bilateral relationship and contribute more to the mutual trust between the two countries," Hong said.