Police in China beat and detained political activists on Sunday marking the 23rd anniversary of the brutal crackdown on the Tiananmen Square democracy protests, 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.

People's Liberation Army soldiers stormed into central Beijing on June 3-4, 1989, firing upon unarmed demonstrators and citizens, killing hundreds if not thousands, as they ended six weeks of democracy protests on Tiananmen Square.

More than two decades later, Beijing still considers the incident a "counter-revolutionary rebellion" and a "political storm" and has refused to acknowledge any wrongdoing or consider compensation for those killed.

The United States urged China Sunday to do more to protect the rights of its citizens and "end the continued harassment of demonstration participants and their families".

State Department deputy spokesman Mark Toner said in a statement that the US remembered the "violent suppression" at Tiananmen Square and urged Beijing "to provide a full public accounting of those killed, detained or missing".

The statement made no specific mention of the latest arrests.

In Beijing, police detained at least 30 activists from eastern Zhejiang province at a railway station Saturday and put them on a bus back to their hometown of Wuxi.

"The police told us it was because of June 4 (the day of the crackdown), that during sensitive periods they had to clean up unstable elements," petitioner Xie Qiming told AFP from the bus.

"No one was beaten, but there were no legal procedures either, they just forced us on to the bus and are sending us home."

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.

In recent days, thousands of people have "strolled" down the main street of Wansheng district, in the southwestern city of Chongqing, in protest against the local government while businesses have been on strike, locals and microblog postings said.

When contacted by AFP, Wansheng police refused to confirm the veracity of photos posted on microblogs showing more than 10,000 people marching on Friday night.

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.

Numerous members of the underground Shouwang Protestant church were also detained by police and prevented from attending a Sunday outdoor service in Beijing due to the sensitive date, members said on a church blog.

The Tiananmen Mothers, a group of relatives of victims of the 1989 crackdown, issued an annual open letter to the government last week calling for the end of communist rule and a reassessment of the official verdict on the protests.

"So long as the Tiananmen Mothers exist, our struggle for justice will not cease," the letter, signed by 121 members, said.

The group has documented the deaths of 203 people killed by soldiers during the crackdown. Thousands were arrested and served time in prison.