Beijing tense on Tiananmen massacre anniversary
Chinese security personnel have swamped Beijing's Tiananmen Square on the 25th anniversary of the Beijing massacre.
Foreign journalists were ushered away from the square and passers-by were searched and had their papers checked.
In recent weeks, the authorities have detained dozens of activists to ensure their silence on the anniversary.
The 1989 protesters wanted political reform, but the crackdown was ordered after hardliners won a power struggle within the ruling Communist Party.
The authorities classify the 1989 protests as counter-revolutionary riots and hold no memorial.
In Hong Kong, however, thousands have gathered in a central park to participate in a Tiananmen remembrance rally.
Activist groups in Taiwan also marked the anniversary by erecting a huge image of Tiananmen Square during the crackdown.
Both the Taiwanese and Japanese governments urged Beijing to use the memory of the protests to improve its attitude to human rights.
In the weeks before this year's anniversary, the Chinese authorities have detained lawyers, journalists and activists.
Rights group Amnesty International said in a statement that 66 people had been detained, questioned or had gone missing.
In a White House statement, the US called on the Chinese authorities "to account for those killed, detained or missing in connection with events surrounding 4 June 1989".
Internet search terms related to the 1989 massacre and the protests have been blocked, and access on Google has reportedly been restricted.
Relatives of those killed in the massacre were allowed to visit the graves of their loved ones under police guard.
The relatives, some of whom campaign for the massacre to be commemorated as part of the Tiananmen Mothers group, told the BBC plain-clothes police were guarding the graveyard and they were told not to talk to the media.
Nobel Peace Prize-nominated rights activist Hu Jia, currently under house arrest, said he regretted not being able to take part in commemorations.
"But it warms my heart that those events and those sacrifices have not been forgotten after 25 years," he told the Associated Press.
- From 1978, China opened up its economy to the world, but communists maintained total control over politics
- In 1989, hundreds of thousands gathered in Beijing's Tiananmen Square to call for political reform
- Protesters remained in the square for weeks while a power struggle raged within the ruling Communist Party
- Hardliners prevailed and gave the order to remove the protesters by force; hundreds were massacred in nearby streets
The protests were the biggest rally against communist rule since the People's Republic was founded in 1949.
Hundreds of thousands called for democratic reforms in a peaceful demonstration largely focused on a gathering in Tiananmen Square.
After six weeks of protests, the authorities responded on 4 June 1989 with a massacre of hundreds in the streets of Beijing.