A Chinese lawyer held after advocating the country adopt a jury system has arrived in the United States after he was detained for several weeks and put under surveillance for months, an American rights group said Tuesday.

Chen Taihe, 45, "was reunited with his family" last week in San Francisco after being informed by police in Guilin that charges against him "would not be pursued", according to a statement by the Dui Hua Foundation.

Police in Communist-ruled China detained Chen last July on charges of "inciting subversion of state power", "provoking a serious disturbance" and "embezzlement", the statement said, during a nationwide crackdown on human rights lawyers and activists that resulted in the detention or interrogation of more than 200.

He was held by police for a month before being put under "residential surveillance in a designated location", a police term that describes imprisonment outside of the country's official system of detention centres and jails.

Later, Chen was allowed to return to his own home and permitted to travel within China, under a form of extra-judicial probation.

After police informed him that charges against him would be dropped, he obtained a Chinese passport and flew to the United States, said Dui Hua, which promotes human rights through dialogue with Chinese authorities.

Before his arrest, Chen published "The Most Common Right", a book based on his study of Britain's judicial system, and was later invited to participate in judicial exchanges in the United States.

"I intend to resume my work promoting the adoption of the jury system in China and look forward to the day when China is a free country that respects individual rights and the rule of law," the statement quoted him as saying.

Detentions such as Chen's have become increasingly common as the ruling party ratchets up controls over civil society under President Xi Jinping.

Last month, UN rights chief Zeid Ra'ad Al Hussein called on China to release lawyers and activists being held "immediately and without conditions".