Activist groups in Hong Kong on Friday urged China for the release of Liu Xia, wife of late Nobel Peace Prize laureate Liu Xiaobo, from illegal house arrest, as they mourned Liu's death and commemorated the ninth anniversary of the release of his democratic reform initiative, Charter 08.

Led by the Hong Kong Alliance in Support of Patriotic Democratic Movements of China, the group pushing for democracy in China and holding annual memorials for the 1989 Tiananmen Square massacre, some 30 people rallied outside the Central Government Liaison Office, Beijing's representative here, calling for Liu Xia's freedom.

"As of now, Liu Xia remained under house arrest and incommunicado," Alliance chairman Albert Ho said. "Liu Xia is absolutely innocent. The abuse and persecution against Liu Xia is unlawful and ruthless. We demand the Chinese government release Liu Xia unconditionally."

He said China has taken a path in the opposite direction from what Liu has advocated in the Charter 08.

"The way Chinese authorities are chasing away the underclass people from the Beijing capital does not show a bit of affection for the people. We believe the authorities will further tighten persecution of the rights advocates and dissidents. Continuing on this path will not bring the country prosperity or stability," Ho said.

The group's secretary general Lee Cheuk-yan said they have been seeking endorsement from legislators locally and in foreign countries, including the European Union, the United States, France, Germany, Australia and New Zealand, to petition Chinese President Xi Jinping for Liu's release.

"Ms Liu Xia has already been under house arrest for seven long years, even though she has committed no crime whatsoever, nor has she ever been sentenced by any Chinese court. (Liu) should not be punished for simply associating with Liu Xiaobo. It is high time that the Chinese government gives back Mr. Liu Xiaobo the recognition and respect he deserved, which the rest of the world already has and to stop suppressing his memory," the petition letter for Xi reads.

Lee said they specifically want Myanmar leader Aung San Suu Kyi, also a Nobel Peace Prize laureate and victim of suppression herself, to speak up for Liu Xia.

"Since Aung San Suu Kyi has endorsed (Xi's ruling of China), she has particularly more responsibility to speak up for Liu, who's simply the wife of a fellow Nobel prize winner and detained for some seven years without being charged of any wrongdoing," Lee said.

The group will release the list of co-signatories of the petition letter next month, while it will also mail some 2,000 Christmas cards with condolences from Hong Kong to Liu, the bereaved families in the Tiananmen crackdown and jailed dissidents in two weeks' time.

Liu Xiaobo, an outspoken critic of China's Communist Party and democracy advocate, was hospitalized in June following a diagnosis of terminal liver cancer, while still serving an 11-year prison sentence for his involvement in drafting the Charter 08, a manifesto calling for an end to one-party rule and a peaceful democratic reform in China.

His wife Liu Xia has been put under house arrest without trial after he won the Nobel Prize in 2010 "for his long and nonviolent struggle for fundamental human rights in China."

China has claimed that Liu Xia's freedom of movement has not been impeded. She appeared in two video footage posted online in August shortly after her husband's death, in which she appealed for "time to heal" and showed the viewers that she has been recovering well.

But her supporters remained worried about her condition and believed she made the video under duress.