VOA Mandarin has attempted to reach Professor Wenguang Sun since he was removed from his home during a live interview earlier this week.
The professor, who lives in Jinan, the capital of eastern China's Shandong province, has not responded. Sources in Shandong told VOA on Thursday that Sun was in a military-run hotel.
On Wednesday, Chinese police broke into the home of the retired Shandong University professor, who is critical of China's human rights record, as he was expressing via a telephone interview his opinions on the Voice of America (VOA) Mandarin television show, Issues & Opinions.
VOA Mandarin has attempted to reach Sun by cellphone and WeChat, a popular social media platform.
In response to the incident, Congressman Chris Smith, a member of the House Foreign Affairs Committee and co-chairman of the Congressional Executive Committee on China, said on Thursday, "In an apparent attempt to chill an open exchange of ideas and opinions, Chinese police may have forcibly stopped a Voice of America interview with Professor Wenguang Sun.
"There is currently no information about Professor Sun's whereabouts, but we urge his immediate release if detained for engaging in what should be his right to free speech," said Smith, who also chairs the House subcommittee on Africa, Global Health, Global Human Rights and International Organizations.
"The Chinese and American people must continue to work toward a day when someone like Prof. Sun can openly share his opinions, via a free press, without fear of reprisal," he added in a statement Thursday.
Senator Marco Rubio on Thursday tweeted: "Every time you hear overblown rhetoric about how we are on the verge of 'tyranny' or 'authoritarianism' in America remember what real tyranny looks like. In #China the police arrested a Xi critic while he was in the middle of a live interview."
A look at Sun's background:
* Born in 1934
* Graduated from Shandong University Department of Physics in 1957, where he stayed on as a teacher
* Detained in "cowsheds" during the Cultural Revolution in the mid-1960s
* Sentenced in 1978 to seven years in prison for "attacking Great Leader Chairman Mao"
* Rehabilitated in 1982, returned to teaching at Shandong University
* Retired from Shandong University in 1994
* Most recent book, A Century of Disasters: From Mao Zedong to Jiang Zemin, published in Hong Kong in 2004
* Passport application denied in 2005, unable to travel aboard since
* One of initial co-signers of Charter 08, a petition for democracy in China
* Shandong University reduced his pension in March
* Criticized China's checkbook diplomacy in an open letter posted on the eve of President Xi Jinping's July trip to Africa
* Police break into his home in Jinan during a live interview with Voice of America on Aug. 1, 2018. Last words via telephone were: "I am entitled to express my opinion. This is my freedom of speech."
Capitol Hill correspondent Katherine Gypson and VOA Mandarin contributed to this report.