A Chinese official sentenced without trial to hard labour for opposing the Maoist revival policies of disgraced politician Bo Xilai has been freed and is seeking compensation, his lawyer said Tuesday.

Ren Jianyu, 25, was released from a re-education through labour camp in Chongqing, the southwestern city Bo used to head, after serving 15 months for attacking his "sing red" campaign, lawyer Pu Zhiqiang told AFP.

Bo is at the centre of the biggest political scandal in China in years, which saw his wife given a suspended death sentence in August for murdering British businessman Neil Heywood.

Bo was kicked out of the ruling Communist Party late last month and is in custody awaiting trial for corruption and abuse of power.

Before the scandal erupted, he had been tipped for promotion to the top ranks of the party at its once-a-decade leadership transition that saw President Hu Jintao hand the top party post to Vice President Xi Jinping last week.

"Ren Jianyu was released from the labour camp on Monday," Pu told AFP by telephone. "The authorities did not give a reason why they released him, but we believe he has been unjustly jailed."

Ren was a local Chongqing official when he was arrested for reposting numerous microblog comments that criticised Bo's "sing red" movement and equated it to the disastrous Maoist "Cultural Revolution" that brought chaos to China from 1966-1976.

Police in Chongqing had initially tried to convict Ren of subversion using a T-shirt of his scrawled with "Give me liberty, or give me death" as evidence.

But Chongqing prosecutors threw out the case and Pu was instead sentenced without trial by police to two years of labour in August 2011.

In China, police can sentence petty criminals to labour camps without trial, a practice widely criticised by rights groups, as well as the United Nations.

Last month, Ren's father sued the Chongqing government, demanding his son be released and reinstated to his job, and given a public apology, Pu said. A Chongqing intermediate court is due to rule on the case Tuesday, he added.

Ren's trial and fate have been widely followed on China's Twitter-like microblog Sina Weibo. Since Bo's downfall, state media have also reported Ren's attempts to seek compensation and restore his reputation.