Police kept Tiananmen Square (search) free of demonstrators Friday, detaining at least 16 people while activists abroad marked the 15th anniversary of the deadly attack on pro-democracy protesters and pressed their demands for political change.

Since the June 4, 1989 military assault that killed hundreds, and possibly thousands, communist leaders have made many changes demanded by the dissidents, scrapping rules dictating where Chinese could work and whom they could marry. A decade of stunning economic growth has given millions new choices in life.

But the closed, secretive ruling party that crushed the protests still permits no independent political activity and has jailed or driven into exile most of China's active dissidents.

Reporters saw 16 middle-aged men and women picked up Friday on the square in twos and threes and dragged to waiting police vans. It wasn't clear whether the detentions were related to the anniversary, but security forces had been trying to block public commemorations for people killed in the military crackdown.

The square was open to the public and hundreds of tourists with their children were strolling under a light sprinkling of rain.

Though extra guards were on duty, security was relatively light compared with other politically sensitive dates. Troops from the paramilitary People's Armed Police (search) dozed aboard two parked buses. Security agents in civilian clothes moved among the crowds.

An Associated Press photographer was briefly detained after photographing detentions on the square, and Chinese tourists who snapped pictures were forced by police to delete them from digital cameras.

In advance of the anniversary, Chinese authorities detained activists and relatives of people killed in 1989 or ordered them out of Beijing (search).

On Friday, broadcasts of news programs to hotels and apartment compounds for foreigners in the Chinese capital were blacked out repeatedly when the network showed reports on the crackdown.

In contrast to the quiet in Beijing, veterans of the protests and other activists commemorated the deaths with vigils, marches and hunger strikes in Hong Kong, Washington and Taipei, Taiwan.

In Hong Kong, thousands of people were expected to attend a candlelight vigil Friday. The anniversary is especially emotional for the former British territory because Beijing recently ruled out full democracy there, stirring fears that it is losing the freedoms and autonomy promised when it returned to Chinese rule in 1997.

In Washington, a veteran of the demonstrations was in the midst of a fast outside the Chinese Embassy that began Tuesday.

"We should not just sit and wait for change. We've been waiting for 15 years and it hasn't happened," said Liu Junguo.

The 1989 protests drew tens of thousands of people to the heart of Beijing to demand a more open political system and an end to official corruption.

The violent government response plunged Beijing into international isolation and set off an upheaval in Chinese politics.

Zhao Ziyang, the Communist Party general secretary, was dismissed after losing a power struggle, and still lives under house arrest 15 years later. Jiang Zemin, a former Shanghai party leader, was plucked from obscurity by then-supreme leader Deng Xiaoping to succeed Zhao and went on to lead China through a decade of stunning economic growth before retiring as president last year.

"Fifteen years has marked tremendous progress economically, but still the biggest obstacle is political," Wu'er Kaixi, a protest leader who survived the 1989 assault, said by telephone from the United States.

On Friday, the New York-based group Human Rights in China released a list of 25 people who it said are still imprisoned in Beijing for taking part in the protests.

Beijing is still trying to repair remaining damage abroad from the bloodshed, lobbying the European Union to lift a ban on weapons sales to China imposed after the crackdown.

Communist leaders are experimenting with what they call "village democracy." Nonpartisan local elections let tens of millions of Chinese pick officials for low-level posts, though winners are required to carry out policies made by unelected figures higher up.

President Hu Jintao, who took power last year, has called for more "socialist democracy." But that means making the party more attentive to public needs, not allowing real opposition politics.

China's leaders defend the crackdown and one-party rule as a key to China's economic success. They reject pleas to reverse the verdict that the protests were a counterrevolutionary riot.

The crackdown "enabled China to develop its economy and make contributions to the peace and development of the world," Foreign Ministry spokesman Liu Jianchao said this week.

On Thursday, Liu refused to say whether student exiles could come home without being arrested. He said they would be dealt with "in accordance with relevant laws."