Pro-democracy activists are marking the 23rd anniversary of the protests that ended with Chinese soldiers opening fire on unarmed civilians, CNN reported Monday.
The Chinese government says 241 people died and 7,000 were injured in the June 4, 1989 protests. Rights groups say the death toll was likely in the thousands.
About a dozen people remain jailed, Human Rights Watch said.
"We encourage the Chinese government to release all those still serving sentences for their participation in the demonstrations, to provide a full public accounting of those killed, detained or missing and to end the continued harassment of demonstration participants and their families," a U.S. State Department statement said Sunday.
"We renew our call for China to protect the universal human rights of all its citizens; release those who have been wrongfully detained, prosecuted, incarcerated, forcibly disappeared, or placed under house arrest; and end the ongoing harassment of human rights activists and their families."
Lu Weimin, spokesman for China's Ministry of Foreign Affairs, said the U.S. accusations are baseless.
"The U.S. side has been ignoring the facts and issuing such statements year after year, making baseless accusations against the Chinese government and arbitrarily interfering with China's internal affairs," he said. "The Chinese side expresses strong dissatisfaction and resolute opposition to such acts."
Chinese rights activist Chen Guangcheng, who has sought refuge in the United States after escaping house arrest, wrote a message to be read Monday to a crowd expected to fill Hong Kong's Victoria Park.
"This Democracy Movement deserves universal approval," he said in the statement. "We ask that its requests be treated appropriately. We do not desire revenge but we want to completely reveal the truth. We are in favor of tolerance but against forgetfulness. People who are forgetful have no future," he said.