More than 50 prominent international authors have written a letter to Chinese president Xi Jinping urging him to free Liu Xia, the wife of deceased Nobel Peace Prize laureate Liu Xiaobo.

The letter, signed by Chimamanda Adichie, Philip Roth, Margaret Atwood, Tom Stoppard and George Saunders, appealed to Xi’s “conscience” and “sense of compassion” to release Liu Xia, who has been under house arrest since 2010 despite never being accused of any crime.

“We urge you to lift all remaining restrictions against Liu Xia, and to ensure her freedom of speech, her freedom to meet with others, and her freedom to travel,” the joint letter said. “Liu Xia has undergone great suffering for many years, simply for being the wife of a man that China has deemed to be a dissident.

“She is in poor health, she is isolated from those who care for her, and she is grieving deeply for the loss of her husband.”

The letter decried her “de facto incommunicado detention” and cited China’s own constitution, which technically guarantees freedom of expression, and the Universal Declaration of Human Rights in appealing for Liu Xia’s release.

She is suffering from heart problems and depression, according to friends who have spoken with her.

Liu Xia was last seen publicly on July 15 in photos of the memorial service for Liu Xiaobo, who died in custody two days earlier. In a video posted to YouTube in July she said: “I am outside recuperating, everyone please grant me time to mourn, time for my heart to heal and one day I will be able to face you all in a healthy state”.

There were concerns at the time the comments were not made of her own free will.

The letter signed by 52 literally and theatre figures was organised by PEN America, a group that advocates for freedom of expression around the world. It was also signed by Teju Cole, Louise Erdrich, Michael Chabon, Chang-rae Lee and Stephen Sondheim. The group also opened the letter to signatures from the public.

“On his upcoming visit to Beijing, we hope President Trump will voice the United States’ concern about the inhumane and unjustifiable detention of a poet who has been accused of no crime,” said Suzanne Nossel, executive director of PEN America.

Trump will visit Beijing from November 8 to 9, but experts doubt he will raise the case of one of China’s most prominent political prisoners.

Liu Xiaobo died at 61 from cancer in July, under heavy police guard in a hospital in northeast China. He was serving an 11 year sentence for “inciting subversion of state power” when he won the Nobel Peace Prize in 2010. His wife Liu Xia was almost immediately cut off from the outside world, confined to her apartment in Beijing.

During a visit by the Guardian to her apartment in July, plain clothes security agent surrounded a reporter within second of arriving, aggressively trying to get the journalist to leave.