Ahead of President Donald Trump's visit to Beijing, literary luminaries such as Margaret Atwood and Philip Roth are calling on China to free the widow of Nobel Peace Prize winner Liu Xiaobo.

A letter issued through the writer's organization PEN America asks that China remove restrictions on Liu Xia's freedom of movement and allow her to meet freely with family, friends and members of the media.

In a news release last week, PEN America Executive Director Suzanne Nossel said the writers hope Trump will "voice the United States' concern about the inhumane and unjustifiable detention of a poet who has been accused of no crime."

Liu Xia has been under unofficial house arrest since Liu Xiaobo was awarded the 2010 prize. Her whereabouts since his July 13 death are unclear.