Human rights advocates say a farm activist in China's Hebei province has disappeared before a visit by Prime Minister Wen Jiabao.

The group Human Rights in China quotes sources in Hebei province as saying that police agents took Zhang Youren away on Tuesday, and beat his wife and son for not cooperating when police tried to search their home.

Sources say Mr. Zhang led a group of farmers petitioning Prime Minister Wen Jiabao for fair compensation for their land, taken to build a reservoir. Li Ping, an attorney with the U.S. based Rural Development Institute in Beijing, says the laws do little to help farmers with grievances.

"There's no kind of procedural guarantees for farmers to voice their concerns for any type of compensation," he said. "Farmers cannot raise their objections if they realize these takings [are] illegal."

Farmer's petitions have become common in China, where thousands have been displaced to make way for massive development projects.

Despite a recent law guaranteeing some tenure security to farmers, petitioners like Mr. Zhang are often rounded up and jailed.

The Human Rights in China group says Mr. Zhang is among 40,000 farmers who were forcibly removed from their plots in the 1990's. While the government did set aside money to compensate them, the petitioners allege the local Communist Party chief, Zhang He, misappropriated the funds.

Zhang He was not available for comment. Police in the town of Tangshan refused to answer questions about Zhang Youren's case and would not confirm whether he had been detained.