"We join others in the worldwide community in urging the Chinese government to make a full public accounting of those killed, detained or missing; to release those who have been jailed for striving to keep the memory of Tiananmen Square alive; and to end the continued harassment of demonstration participants and their families".
The Chinese government sent tanks to quell the June 4, 1989 protests, and has never released a death toll.
Human rights groups and witnesses estimate that those who died ranged from several hundred to several thousand.
He cited Chinese dissident Liu Xiaobo, who wrote in his 2010 Nobel Peace Prize speech, delivered in absentia: "The ghosts of June 4th have not yet been laid to rest".
"We join others in the global community in urging the Chinese government to make a full public accounting of those killed, detained or missing", Pompeo's statement said.
China's door to talks is open in principle, its Foreign Ministry said yesterday, a day after Beijing warned that any trade and business deals reached with Washington would be void if the United States implemented tariffs.
Several other speakers blasted the "one-party democracy" China has imposed on Hong Kong and referred back to the Umbrella Revolution of 2014, a youth-driven democracy protest that continues to engage the sympathies of young people in Hong Kong long after Beijing assumed it had been crushed.
Chow's speech says: "They want us to accept this reality: China is under the rule of the Communist Party, and the regime is going to last forever".
Today, 4 June 2018, marks the 29th anniversary of China's brutal squelching of student pro-democracy protests.
A public opinion poll by the University of Hong Kong found that the proportion of people who think Hong Kongers have "a responsibility to instigate the development of democracy in China" has dropped from 58 percent to 56 percent this year.
Security has been tightened at the square and the surrounding area in central Beijing.
Hong Kong is the only place in China where such large-scale public commemorations happen, though neighbouring Macau also holds smaller annual gatherings.
Foreigners' passports were checked by Chinese police at a checkpoint almost a kilometre from the square.
In Taiwan, the democratic island nation that is increasingly threatened by Beijing's aggression, President Tsai Ing-wen also commemorated the anniversary and said in a Facebook post that she hopes "both sides of the Taiwan Strait can enjoy the universal values of freedom and democracy".