The Chinese government is responsible for the "enforced disappearance" of Liu Xia, the widow of late Nobel peace laureate Liu Xiaobo, her US-based lawyer has said in a formal complaint filed with the UN.

Liu Xia has been "held incommunicado in an unknown location by Chinese government authorities" since July 15, the day of her husband's funeral, he lawyer, Jared Genser, said in statement to the UN working group on enforced or involuntary disappearances on Wednesday.

China faced a global backlash for its treatment of Liu Xiaobo when he died of liver cancer last month, making him the first Nobel Peace Prize laureate to die in custody since 1938 when German pacifist Carl von Ossietzky died while being held by the Nazis.

Liu Xia, 56, was followed around the clock by security officials, and has not been in touch with anyone since about a day before her husband's death, Genser said.

"I demand that Chinese authorities immediately provide proof that Liu Xia is alive and allow her unhindered access to her family, friends, counsel, and the international community," he said in a separate statement emailed to AFP news agency.



Genser said international law defined "enforced disappearances" as situations where government officials are involved in depriving a person of her freedom against her will, and refuse to acknowledge that deprivation or conceal the disappeared person's fate.

He said all such conditions had been met in Liu Xia's case.



The UN working group did not acknowledge the receipt of Genser's complaint, but told AFP news agency that generally speaking, its process of issuing an "opinion" on the matter was a lengthy one that could take years.



China would be free to dismiss that non-binding outcome.

International pressure

The US, the European Union and the UN High Commissioner for Human Rights have called on China to free Liu Xia, who had been under house arrest since Liu Xiaobo won the Nobel prize seven years ago, despite having never been charged with a crime.

Last month, Germany said it was "deeply concerned" over what it called China's "unwillingness to discuss lifting restrictions" against Liu Xia, a source told Reuters news agency.

In 2011, the UN working group on enforced or involuntary disappearances said that "deprivation of liberty of Liu Xia ... is arbitrary".

Zhang Qingyang, a Chinese government spokesman, declined to disclose Liu Xia's whereabouts on July 15, saying only that it was "best for her not to receive too much outside interference during this period.

"The relevant departments will protect Liu Xia's legal rights according to law," he said.

Chinese authorities have also said she is a free citizen who has been merely too grief-stricken by her husband's death to be in touch with any friends or counsel.

Foreign journalists who have tried to visit the couple's Beijing home have been rebuffed and physically harassed.

READ MORE: Is China afraid of Liu Xiaobo's legacy?

Seven people are currently detained by Chinese police for commemorating Liu Xiaobo, the Chinese Human Rights Defenders said on Wednesday.

Authorities released photographs and a video of Liu Xia at what rights groups have called a "heavily scripted" funeral and sea burial of her husband.

Liu Xiaobo was a veteran of the 1989 Tiananmen Square protests who was jailed in 2008 after co-writing a petition calling for democratic reform, and sentenced to 11 years in prison for "subversion" a year later.

He was diagnosed with late-stage liver cancer in May.

In June, he was granted medical parole and moved to a hospital in Shenyang, where he was reportedly treated in an isolated ward under armed guard.

China resisted strong international pressure to allow Liu Xiaobo to seek treatment abroad.