The United States is calling for China to provide immediate medical treatment to the imprisoned nephew of Chinese activist Chen Guangcheng.

The nephew, Chen Kegui, is suffering from appendicitis but being denied medical parole, according to human rights groups and his father.

They say he has been subject to mistreatment in custody.

Human Rights Watch said on Tuesday that the treatment is inadequate and threatens his life.

"To deny him appropriate treatment reflects at best incompetence and at worst a twisted effort to torment the Chen family," the group's China director, Sophie Richardson, said.

Calls to the prison in Linyi, in eastern China, and to the prison hospital rang unanswered on Tuesday, a holiday.

"We remain deeply concerned by reports [of] mistreatment in prison and of his acute medical condition," State Department spokesman Patrick Ventrell told reporters in Washington.

He said US Ambassador Gary Locke raised the case at the Foreign Ministry in Beijing on Tuesday.

Ventrell said the US was also concerned by credible reports that local authorities continue to harass the detainee's family members in his home village.

Chen Kegui was sentenced in November to three years in prison in the aftermath of his uncle's escape.

Source: Agencies