China has detained at least three farmers on subversion charges for making bold calls for private land ownership in the countryside, an attempt to curb land seizures by corrupt officials, their families said on Monday.

Police in Huayin in the northwestern province of Shaanxi made the "criminal detentions" earlier this month, suspecting the three of "inciting to subvert state power", Ruan Xiuqin, wife of Chen Sizhong, one of the farmers, told Reuters by telephone.

Chen, Zhang Sanmin and Xi Xinji were among the six peasants who signed an open letter declaring that 70,000 farmers in the region enjoyed permanent private ownership of 10,000 hectares of collective land, said Ruan and Liu Cuiying, Zhang's wife.

"We reject the previous form of collective ownership. It cannot guarantee the farmers' permanent rights to the land ... and cannot prevent the illegal infringement by officials and thugs," reads the letter, a copy of which was seen by Reuters.

China's constitution stipulates that for its 750 million rural dwellers, farm land is owned either by the state or by the collective–normally in the form of a village or a township.

Under the collective ownership system, farmers are vulnerable to land being expropriated by local officials who pocket the gains, a practice which has incited some of the country's most violent protests in recent years.

But peasant complaints in the past have revolved around compensation standards, corruption and lack of transparency, rather than challenging the collective ownership policy itself.

It is not known how many locals really support their land claims, but farmers in at least two other provinces have recently made similar appeals on private ownership.

Yu Changwu from the northeastern province of Heilongjiang has urged the ruling Communist Party to honour its "revolutionary ideals and pledges" and hand land back to the farmers.

"We peasants have been fed up with the fate of being plundered and trampled on ... Only by truly owning the land can we have a secure life," Yu and another farmer wrote in a separate open letter.

Beijing launched violent land reforms after the Communist revolution in 1949, benefiting many poor farmers, but radical collectivisation soon followed.

Individual farming was reintroduced in the 1980s, but rural residents still only enjoy "usage rights" under long leases, rather than full ownership.

Land privatisation is a sensitive subject for the Communist government, which despite market reforms of the past 30 years still has ideological concerns.

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