US calls for China to protect the "universal human rights of all its citizens" and to release all Tiananmen prisoners.
The United States has called on China to release all prisoners still detained for their involvement in pro-democracy demonstrations 23 years ago.
Sunday’s move came on the anniversary of the crackdown that ended the demonstrations centred around the capital's Tiananmen Square.
The statement released by US Department of State Deputy Spokesman Mark Toner also called on Beijing to "provide a full public accounting of those killed, detained or missing; and to end the continued harassment of demonstration participants and their families."
"We renew our call for China to protect the universal human rights of all its citizens," it said.
On July 4, 1989, the Chinese military dispersed pro-democracy demonstrators using tanks and live ammunition. No official toll has been provided, but estimates range from hundreds to more than 1,000 killed, with around 10,000 injured and thousands detained.
Police in China beat and detained political activists on Sunday marking the 23rd anniversary of the brutal crackdown, rights campaigners said.
Officers used violence against activists in the southeast province of Fujian and detained them, while more than 30 people who came to Beijing "to petition" were held and forced to return to their home province, the activists reported.
"Around 20 rights defenders were stopped by police and beaten this morning on May First Square," Shi Liping, the wife of activist Lin Bingxing, told AFP by phone from Fuzhou, capital of Fujian province.
"The police said they were going to 'beat them to death'. They took about eight people into custody, including my husband. I fear he has been beaten badly."
Police in Fuzhou contacted by AFP denied anyone had been detained.
Any mention of the 1989 protests is banned in state media and the subject is largely taboo in China.
But the overseas dissident website www.molihua.org has in recent days urged those opposed to the crackdown to dress in black and "stroll" in public places throughout China on June 3-4.
The call, which spread through numerous microblogs, was similar to ones last year urging Chinese to hold protests akin to those that spread through the Arab world.
Veteran dissident Hu Jia said on his microblog that, as in previous years on June 3-4, police had stepped up security around the homes of numerous political activists and social critics in Beijing.
Rights activists and lawyers said police had also contacted them and warned against participating in activities marking the crackdown.