* Authorities say Xue Fushun jumped to his death
* Lawyer for family says he might have been murdered
* Parents detained to pressure activist son-rights group
By Michael Martina
BEIJING, Feb 4 (Reuters) - The death of a Chinese pro-democracy campaigner's father is being disputed by his family, a lawyer and a rights group said, after being told by authorities that he committed suicide while in detention.
A statement from advocacy group Human Rights in China, which was confirmed by a lawyer for the family, said the parents of activist Xue Mingkai were detained on Jan. 23 in Qufu city in the eastern province of Shandong.
It contested what it said were accounts by public security authorities that Xue's father, Xue Fushun, had killed himself by jumping from the fourth floor of a prosecutor's building.
"This case involves an unnatural death. Many people suspect that it was premeditated murder," Tang Jitian, a lawyer for the family, told Reuters by telephone.
After being held for six days, Xue and his wife, Wang Shuqing, fled and sought protection at a local prosecutor's office but were caught and separated. Days later, Wang was informed by authorities that her husband was dead.
"What's key now is that the police and relevant departments there handle this in a transparent manner," Tang said. "If it truly was suicide, then they should accept questions and address public suspicion under the sunlight."
Xue Mingkai, 24, a member of the banned China Democracy Party, was released in September after serving a total of four years in prison on separate convictions of "subverting state power" and "inciting subversion of state power".
According to the human rights group, his parents were being held in an attempt to pressure their son to return to the city.
Tang said the family had been unable to follow the case because of Xue's harassment by authorities due to his pro-democracy activities and his mother's detention.
"At the very least, because of his mother's status as a legal citizen, this behaviour constitutes illegal detention and quite possibly a more serious crime," he said.
Authorities in Qufu could not be reached for comment.
An open letter from the family's supporters calls for a transparent investigation of what it suggests is a pattern of abuse.
"Dissidents are in fact not protected by the law while stability maintenance departments can violate their human and civil rights at will, even going as far as persecuting their family members," the letter said.
China defends its human rights record and rejects criticism from foreign groups and governments, saying it guarantees its people wide freedoms and has lifted millions out of poverty.
A once-in-a-decade leadership change in China in late 2012, which brought Xi Jinping to power as Communist Party chief, inspired many Chinese with hope for political reform.
But a spate of detentions and convictions of activists has signalled that the ruling Communist Party will not tolerate any open challenge despite promises of greater transparency.
A court sentenced one of China's most prominent rights advocates, Xu Zhiyong, to four years in prison in late January after he campaigned for the rights of children from rural areas to be educated in cities and for officials to disclose their assets.
China has detained at least 20 campaigners demanding asset disclosure by officials in recent months, though not all belong to the New Citizens' Movement, founded by Xu, which advocates working within the system to press for change.
Xu's sentence was followed by the conviction of another two anti-graft campaigners in Beijing, which drew criticism from the United States and Europe. (Reporting by Michael Martina; Editing by Alistair Lyon; )