The United States is "deeply disturbed" by reports of the death of prominent Chinese human rights activist Cao Shunli, detained in September for staging sit-ins at the country's foreign ministry, the State Department said on Saturday.

The news of her death came on Friday, soon after the start of a session in Geneva of the UN Human Rights Council, a body to which China was elected amid controversy last November.

We offer our condolences to her family - U.S. State Department spokeswoman, Jen Psaki

"The United States is deeply disturbed by reports that rights activist Cao Shunli has passed away at a hospital in Beijing. We offer our condolences to her family," State Department spokeswoman Jen Psaki said in a statement.

Cao staged a two-month sit-in along with other activists outside the Foreign Ministry, beginning in June, to press for the public to contribute to a national human rights report.

Authorities prevented her from flying to Geneva for a human rights training program in September. She was formally arrested in October on suspicion of "picking quarrels and provoking troubles," the watchdog group Human Rights in China said.

Denied parole

Human Rights in China had quoted Cao's lawyer last month as saying she suffered from tuberculosis, liver disease and other ailments. Medical parole was denied until she was seriously ill.

Cao died in a Beijing hospital to which authorities had finally let her be taken, according to one of her lawyers, Wang Yu, and a dissident, Hu Jia.

Cao's younger brother, Cao Yunli, told Reuters on Sunday that the family was seeking answers about her death, and were still considering whether to sue the detention centre where she had been held before being moved to a Beijing hospital.

"The family needs an explanation how this could have happened," he said by telephone. "Tuberculosis isn't a new or special disease — it ought to be able to be treated."

Reuters was unable to reach the detention centre where Cao Yunli had been locked up for comment.

Hundreds of activists along with Cao had urged officials to reply to their requests to participate in drafting China's national human rights report ahead of the country's Universal Periodic Review by the United Nations in October.

"We continue to be concerned about the human rights situation in China and will continue to urge Chinese authorities to guarantee all Chinese citizens the protections and freedoms to which they are entitled under China's international human rights commitments," Psaki said.