Authorities in China have forced Liu Xia, the widow of dissident and Nobel laureate Liu Xiaobo, to disappear, the couple’s attorney claimed on Wednesday. Xiaobo died on July 13. In a formal complaint lodged with the United Nations, Washington-based human rights lawyer Jared Genser said China was guilty of Liu’s “enforced disappearance”, The Guardian reported.

Liu’s whereabouts have been kept secret since her husband died of cancer while in government custody. Her friends alleged that authorities had taken her away fearing that she would attract support even under house arrest, according to The Times.

In his complaint, Genser has sought the United Nations’ “urgent intervention”, pointing out that the Liu’s disappearance suggested the “involvement of government officials” and their “refusal to acknowledge the deprivation of liberty”.

Liu was last seen in a few photographs of her husband’s sea burial. The photos were released on July 15. “There has been no information as to where she is, who is detaining her or when she might reappear,” the attorney told The Guardian. “It is clear to me...that the Chinese government has her.”

Her husband died while serving an 11-year sentence for writing a pro-democracy manifesto called Charter 08, where he called for an end to one-party rule in China. Liu Xiaobo had been jailed multiple times through his life.