BEIJING—China has detained several dissidents and campaigners ahead of US President Barack Obama's much-anticipated first visit to the country, their relatives and close contacts told Agence France-Presse Saturday.

Obama arrives in Shanghai on Sunday and moves onto Beijing the next day for a four-day maiden presidential trip during which he has been urged to raise human rights with the Asian giant's top leadership.

But as the visit drew close, the head of an activist group for parents whose children were sickened by tainted milk in China had been detained, his wife told Agence France-Presse.

"Zhao Lianhai was criminally detained for 'provoking an incident'," Li Xuemei said in a text, without giving further details.

According to activist group Human Rights in China, Zhao was handcuffed and taken away late Friday night by police officers who searched his house and took away computers, a video recorder, a camera and an address book.

When Zhao refused to go with them, as the summons did not state a cause, the police officers filled in "provoking an incident" in the summons, the group said. Police in Beijing would not comment on the case.

Zhao has campaigned relentlessly for parents whose children suffered from drinking milk tainted with the melamine chemical, which killed six children and sickened nearly 300,000 others in a scandal that erupted in September 2008.

Qi Zhiyong, a dissident who lost a leg during the crackdown on the 1989 Tiananmen democracy protests, said he had also been detained for trying to organize a human rights seminar on November 9 in a Beijing park.

In a text sent to AFP, Qi said he and fellow organizers had planned for the seminar to last until the end of Obama's visit.

He had also applied to police to protest the US President's visit, "to press him to pay attention to human rights in China, people's livelihoods and the relatives of jailed people, as he comes only to talk about climate change."

Qi said he was being held in the Beijing suburbs and had been charged with unlawful assembly and disturbing the social order.

He added that Li Jinping, who every year tries to organize commemorations of deposed former leader Zhao Ziyang, who opposed the use of force to quell the 1989 protests, had also been detained.

Yang Qiuyu, a housing rights activist, and more than 30 other petitioners had also been taken away, Qi said.