Hong Kong spy-case scholar Li Shaomin has urged the mainland to free an SAR academic who has been jailed for 13 years for revealing state secrets. The SAR-based Information Centre for Human Rights and Democracy says Hong Kong permanent resident Dr Xu Zerong was sentenced by Shenzhen Intermediate People's Court last month. He was convicted of 'illegally supplying national secrets' to a person in Hong Kong and an 'illegal operation' for selling Hong Kong periodicals on the mainland. Xu, 46, a Zhongshan University researcher who used to publish a social science journal in Hong Kong, was arrested on the mainland in August 2000. He is to appeal against the conviction. Another Shenzhen scholar, Professor Shi Xianmin, 47, has been jailed for two years for transferring an 'internal reference' document eight years ago to his friend Dr Li, the City University lecturer convicted of spying for Taiwan last year. Shi, who taught micro-economics and demography at the Shenzhen Communist Party School, might seek medical parole. He was arrested last April. Dr Li - who was expelled to the United States after being convicted by a Beijing court in July and has since returned to his teaching post in Hong Kong - said the sentences were 'inconceivable' as the two scholars were only doing social research. 'They are innocent,' he said. 'They were just doing social research which did not involve any national secrets whatsoever.' Dr Li said national secrets were vaguely defined and unpredictable and scholars had no guidelines to follow. 'What damage has been done by them? It seems national secrets are nothing but things China doesn't like,' he said. Dr Li said he could not recall what he was given by Shi, but believed it was only some details from a newsletter about social analysis. According to the information centre, Xu was convicted of illegally obtaining and transferring four copies of confidential documents about decisions made by Chinese leaders on the deployment of volunteer armies during the Korean War. Frank Lu Siqing, the centre's spokesman, said Xu came from a family with close ties to the Communist Party and the PLA. His mother in Guangzhou told TVB that the family had been informed of the verdict. She admitted there might be some information about the Korean War at home, but it was of little 'publishing value'. Xu has a 16-year-old son who is studying in Hong Kong. Ong Yew-kim, research fellow of Chinese Law at Chinese University, said the heavy sentence was expected. 'If all children of senior cadres went back home after studying overseas and took away confidential information, it could mean very big trouble,' he said. The Security Bureau said it had not received any request for help from Xu's family. Xu, who gained a PhD from Oxford University in England, has written articles on China's role in the Korean War that were published in a Princeton University journal in 2000. One month before his arrest, Xu also published an article in Chinese-language magazine Yazhou Zhoukan about Chinese aid to the Malayan Communist Party between 1960 and 1980.