FILE PHOTO - Liu Xia, the wife of Chinese dissident Liu Xiaobo, talks to the media in Beijing

Beijing - Friends of China's Nobel laureate Liu Xiaobo, who died as a political prisoner, say they are worried about his widow, Liu Xia, whom they haven't been able to contact since the funeral.

Authorities say Liu Xia is "free," but friends fear she is still under supervision because they are not able to contact her. She has been under house arrest with no charges since 2010, when Liu was awarded the Nobel Peace Prize for his work campaigning for human rights in China.

"Liu Xia is free so far, and we want her to avoid trouble because she was in grief after losing a relative," Zhang Qingyang, a spokesman for authorities in the northern city of Shenyang, said Saturday.

Liu was buried at sea on Saturday by friends and family, including Liu Xia, according to state media.

But several friends told dpa on Monday they haven't been able to reach the 56-year-old poet, who reportedly suffers from depression and a heart condition.

"Of course we are all very worried about Liu Xia," said friend and activist Hu Jia. "I don't think she is back in Beijing. I haven't been able to get in touch with her."

Authorities might decide to extend her house arrest, said friend Ye Du.

Liu died on Thursday of multiple organ failure, according to authorities. He was being treated for terminal cancer under medical parole. When he died, he was approaching the end of an 11-year prison sentence for subverting state power.

Since Liu's death, foreign officials including US Secretary of State Rex Tillerson and UN rights chief Zeid Ra'ad Al Hussein have called on Chinese authorities to end Liu Xia's house arrest and allow her to move overseas.