A prominent human rights lawyer who has been prevented from leaving the country by the ruling Chinese Communist Party says the ban is linked to his defense of a fellow attorney detained in a nationwide crackdown begun in July 2015.
Chen Jiangang was prevented from boarding a flight to Seattle by border guards at Beijing's International Airport on Monday. He was en route to take up a Humphrey Fellowship funded by the U.S. State Department.
A State Department spokeswoman urged China to let Chen travel.
"We are disturbed by reports that Chinese authorities prevented prominent human rights lawyer Chen Jiangang from leaving China to participate in a State Department-sponsored exchange program," spokeswoman Morgan Ortagus said via Twitter.
"We urge China to respect Chen's freedom of movement and to view lawyers and rights defenders as partners in strengthening Chinese society through development of rule of law," she said.
Chen told RFA that Beijing police, who ordered the ban, had since given him a fuller explanation.
"The first reason was my defense of Xie Yang, who was detained in the July 2015 crackdown," he said. "They still hate me for doing that."
"The second thing is their hatred and hostility towards the U.S. government," he said. "[President] Xi Jinping has never announced that America is our enemy, so there is no basis whatsoever for such a ban on me as an individual, nor to extend that ban to my entire family of four people."
Chen had been chosen to study English as part of the Humphrey Fellowship Program that was first announced by then-President Jimmy Carter in 1978 to finance studies at U.S. universities and institutions embodying the values of "democracy, social justice and a desire to assist the developing nations of the world," according to the program's official website.
Chen, his wife, and the couple's two children were all added to an earlier exit ban "blacklist" in 2017. The family was also detained and forcibly escorted back home from a vacation in the southwestern province of Yunnan in the same year.
Fellow rights lawyer Wang Yu, one of the first lawyers to be detained in July 2015, and who remains under police restrictions since her release, said the crackdown is ongoing.
"A lot of the lawyers detained since July 2015 and their defense attorneys have been prevented from leaving the country, along with their families," Wang said. "The crackdown ... is still going on, not just through detentions, but also through restrictions on people's personal liberty, including travel bans."
Chinese foreign ministry spokesman Lu Kang said on Thursday that the exit ban on Chen and his family was "in accordance with China's own laws."
"China's relevant departments are ... handling the exit-entry affairs of the relevant Chinese national in accordance with the law," Lu told a regular news briefing in Beijing.
Chen was instrumental in exposing the torture of Xie Yang, who was initially detained on July 11, 2015, then held under "residential surveillance at a designated location" in a government guesthouse belonging to the National University of Defense Technology in Hunan's provincial capital, Changsha.
Subjected to abuse including deprivation of food and water, Xie was tortured again after being moved to the police-run Changsha No. 2 Detention Center following his formal arrest on Jan. 9, 2016.
Xie was subjected to confinement in a "hanging chair" made of plastic chairs stacked high above the ground for hours at a time, so that his legs swelled up and he was in excruciating pain, he told his lawyers.
He was also deprived of sleep and repeatedly beaten, humiliated, and taunted with death threats against his family, according to copious and detailed notes made public from meetings with his lawyers, including Chen.
Reported by Ng Yik-tung and Sing Man for RFA's Cantonese Service, and by the Mandarin Service. Translated and edited by Luisetta Mudie.