Hundreds of thousands of people took part in vigils in Taiwan and Hong Kong on Saturday to mark the 22nd anniversary of China's crackdown on pro-democracy protesters in Tiananmen Square, as authorities in the mainland rounded up dissidents to try to quell any possible demonstrations there.

As usual, the Tiananman anniversary was ignored by China's state controlled media, and there was heavy security around the square in Beijing.

The Foreign Ministry in Beijing, meanwhile, lashed out at the U.S. government over calls for a full accounting of the military assault on civilians on June 4, 1989, saying the issue was closed.

"A clear conclusion has already been made concerning the political turmoil that happened in the late 1980s," spokesman Hong Lei was quoted as saying by the official Xinhua news agency.

Stricter measures against dissidents are routine on the June 4 anniversary, but this year they coincide with the most sweeping suppression campaign in many years. Hundreds of activists, lawyers and bloggers have been questioned, detained or simply have disappeared in the four-month campaign that aims to quash even the possibility of a pro-democracy movement forming along the lines of those sweeping the Arab world.

Nobel Prize put rulers on edge

China has been on edge since imprisoned dissident Liu Xiaobo was awarded the Nobel Peace Prize last October. The country strongly cautioned the Norwegian Nobel committee against giving the honour to the pro-democracy leader. In a sign of the depth of the current crackdown, Chinese police in early April arrested artist Ai Weiwei, who had been thought to be immune to state interference and was one of the designers of the main stadium for the 2008 Olympics in Beijing.

"We are witnessing the darkest age for China's human rights, with suppression of human rights defenders everywhere in China since the Nobel Peace Price for Liu Xiaobo and the Jasmine Revolution," said Lee Cheuk-Yan, a pro-democracy leader based in Hong Kong, a semi-autonomous part of China where residents enjoy more freedoms. "So we are … going to give a very very strong message to stop suppression, release Ai Weiwei and all other human rights defenders. And the movement in Hong Kong will continue in our struggle until democracy wins over a one-party state."

Children hold candles during a Saturday's vigil in Hong Kong. China continued to roundup of political dissidents in the lead-up to the anniversary. (Ed Jones/AFP/Getty Images)

More than 150,000 pro-democracy demonstrators held a candlelit vigil in Hong Kong on Saturday. Activists laid a wreath at a makeshift memorial and bowed three times as is customary in Chinese mourning tradition. The crowds watched video messages from Wang Dan, one of the 1989 movement's leading voices, and Ding Zilin, of the "Tiananmen Mothers" activist group that represents people who say they lost relatives in and around Tiananmen Square in 1989.

Wang, a Chinese pro-democracy activist and former student leader, is in exile in Taiwan, where he attended a commemoration event on Saturday. He said Taiwan has an "undeniable duty" to promote democracy in China but has been relying too much on "words without action."

"The Chinese government is still severely suppressing people as a caution to anyone seeking to express political opinions, often even in cases where ordinary individuals are just appealing about their house being torn down or land taken away," he said.

Hundreds of people attended the rally and vigil at Liberty Square in Taiwan's capital, where they watched musical performances, held up signs and listened to speeches.

The Chinese government has never fully disclosed what happened when the military crushed the weekslong Tiananmen protests, which it branded a "counterrevolutionary riot." At least hundreds, and possibly as many as 1,400 people, were killed when troops backed with tanks fought their way to the square into central Beijing on the night of June 3-4.

With files from The Associated Press