Authorities in the Chinese capital have imposed a travel ban on a prominent liberal economist who had been invited to take part in a Harvard symposium this month after his independent think-tank was subjected to a series of police raids.
Sheng Hong, the director of an independent Chinese think tank, has been barred from leaving the country to attend a seminar at Harvard University on the grounds that he would "endanger national security", as Beijing continues to silence liberals critical of its policies.
Sheng Hong, executive director of the Unirule Institute of Economics, had been due to attend the event examining China's 40 years of economic reforms.
But he was barred from boarding a flight to Chicago last week by police at Beijing's Capital International Airport, who said his departure would "harm national security."
"They told me I was suspected of 'harming national security'," Sheng told RFA on Monday, adding that he had asked for the reason for the move.
"[The policeman] told me he had just been tasked with conveying this decision to me, and so he was unable to answer my question, which was: 'In what way does my attending a symposium harm national security?'" Sheng said.
"He couldn't answer me, or didn't want to," he said. "There is no basis for this."
Sheng said he has still received no explanation for the decision, which was handed down to the Beijing police department by China's cabinet, the State Council.
He said his recent articles have offered nothing but constructive economic suggestions, and fall within the freedom of speech that is enshrined in China's constitution.
Sheng said he had responded to the travel ban by penning a letter to China's President Xi Jinping.
"I wrote asking Mr. Xi to rectify the situation, but I haven't had any response," he said. "I never thought that, 40 years after economic reforms began, attending a symposium would be regarded as harming national security."
Constitutional scholar and independent historian Zhang Lifan said the symposium had been planned jointly by Unirule and Harvard.
"Obviously, everyone is going to have a different interpretation of the 40th anniversary since the start of economic reforms," Zhang said. "Why is the official view the only one allowed to be heard?"
In July, the authorities welded shut the front door of the liberal-minded Unirule Institute of Economics, trapping five members of staff, a move commentators said is part of a long-term strategy by the ruling Chinese Communist Party to limit the freedom of expression of Chinese intellectuals.
The staff members were illegally detained for more than an hour, and had to call the police to be able to exit the premises. Nobody has been able to gain access to the offices since.
The institute was founded in 1993 by liberal economist Mao Yushi, who has repeatedly challenged the government on its economic policy and was awarded the Milton Friedman Prize for Advancing Liberty in 2012.
Since taking power in 2012, President Xi Jinping has launched an unprecedented set of ideological controls and boosted the institutions needed to enforce them.
Xi has repeatedly warned members of the political class not to go off message in public, and set up a nationwide monitoring agency to supervise and detain anyone remotely connected with the government, including civil servants, teachers and academics, journalists, and contractors.
The closure of Unirule came after the closure of the liberal political magazine Yanhuang Chunqiu and the outspoken analysis website ConsensusNet, both of which had specialized in wide-ranging political and economic analysis.
Unirule's website was also shuttered in January 2016, and the social media accounts of some of its prominent members deleted.
Reported by Gao Feng for RFA's Mandarin Service, and by the Cantonese Service. Translated and edited by Luisetta Mudie.
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