The daughter of Ilham Tohti, a Uighur intellectual who is imprisoned in China, has said she does not know if her father is alive.
Jewher Ilham made the remark after accepting a top European human rights prize on behalf of her father.
Ilham Tohti was jailed for life on separatism charges in 2014.
China has provoked an international outcry over alleged mass detention of Uighurs, an indigenous Muslim minority, in the western Xinjiang region.
Ms Ilham said she has not seen her father since 2013 and has had no communication with him for two years.
He was awarded the European Parliament’s Sakharov Prize for Freedom of Thought for promoting “dialogue and mutual understanding” between the Uighur and other Chinese people.
Ms Ilham said her father had been labelled “a violent extremist, with a disease that needs to be cured and mind that needs to be washed”.
Mr Tohti set up a website – UighurOnline – to educate both Chinese and Uighur speakers about social issues.
“I am grateful for the opportunity to tell his story, because he cannot tell it himself,” said Ms Ilham, who received the award next to a symbolic empty chair. “To be honest with you, I do not know where my father is. 2017 was the last time my family received word about him.”
Beijing insists that everyone has now “graduated” and been released from what they call “re-education camps” – claims that have not been verified due to China’s strict control on the media.
“Today should be a moment of joy to celebrate freedom of speech,” said the parliament’s president David Sassoli in Strasbourg. “Instead, it is a day of sadness. Once again, this chair is empty, because in the world we are living, exercising our freedom of thought does not always mean being free.”
Ms Ilham said she drew hope from last year’s Sakharov prize winner, Oleg Sentsov, a Ukrainian film director who was imprisoned on terrorism charges and released in November.
“I hope the same thing happens with my father,” she said.