BEIJING -- China's health authorities will investigate allegations that genetically modified rice was tested on Chinese children as part of a Sino-U.S. research project, state media said Tuesday.

One Chinese researcher has been suspended by authorities while investigations are carried out.

China is already the world's largest grower of genetically modified (GMO) cotton and the top importer of GMO soybeans but, while Beijing has already approved home-grown strains of GMO rice, it remains cautious about introducing the technology on a commercial basis amid widespread public concern about food safety.

The Chinese Center for Disease Control and Prevention investigation came after a report last month by environmental group Greenpeace claimed that a U.S. Department of Agriculture-backed study used 24 Chinese children aged between six and eight to test genetically modified "golden rice."

Golden rice, a new type of rice that contains beta carotene, is intended to alleviate vitamin A deficiency.

The Chinese Center for Disease Control and Prevention said no domestic institutions had been approved to participate in the research and that it had also asked Tufts University outside Boston to help investigate the issue.

The International Rice Research Institute is working with leading nutrition and agricultural research organizations to develop and evaluate golden rice as a potential method to reduce vitamin A deficiency in the Philippines and Bangladesh.

The research by Tufts University and other Chinese scientists was published in the American Journal of Clinical Nutrition in August. It aimed to demonstrate that the rice could provide a good source of vitamin A for children in countries where deficiency in the vitamin is common.

Complete China coverage on NBCNews.com's Behind The Wall

Tufts reviews protocols
Andrea Grossman, assistant director of public relations at Tufts University, told state news agency Xinhua in a recent interview the university was deeply concerned about the allegations and is reviewing protocols used in the 2008 research "to ensure the strictest standards were adhered to."

"We have always placed the highest importance on human health, and we take all necessary steps to ensure the safety of human research subjects," Grossman said.

More coverage about food safety on NBCNews.com

"We have always been and remain committed to the highest ethical standards in research," she said.

The Greenpeace report sparked a wave of criticism on Weibo, China's version of Twitter, with the researchers accused of a breach of ethics for testing poor, rural children whose families may not have been informed properly.

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Scientist suspended
One of the Chinese authors, Shi-an Yin, has been suspended from work pending further investigation after his responses proved to be inconsistent, the Chinese Center for Disease Control and Prevention said.

Yin was cited by the official People's Daily newspaper as saying he helped collect data for the study but was unaware that it involved GM rice.

The second of the two Chinese researchers, Hu Yuming, denied his involvement in the research, the People's Daily said.

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China, the world's top rice producer and consumer, approved the safety of one locally developed strain of genetically modified rice, known as the Bt rice, in 2009, but commercial production has been delayed.

Apart from genetically modified products, China's vast and unruly food sector is still struggling to come to grips with food safety four years after a major scandal where tainted milk powder was blamed for the deaths of at least six children.

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Andrew Kelly / Reuters

Protesters lay in front of a mock tank as part of a demonstration in New York on Sunday to mark the 23rd anniversary of the The Tiananmen Square protest in China.

The United States urged China to free all those still jailed over the 1989 Tiananmen Square pro-democracy demonstrations on the 23rd anniversary of the brutal crackdown.

State Department deputy spokesman Mark Toner issued a statement late on Sunday calling on the Chinese government on Sunday "to provide a full public accounting of those killed, detained or missing."

The statement said the U.S. "joins the international community in remembering the tragic loss of innocent lives" -- a comment unlikely to be welcomed by China’s ruling Communist Party.

Hundreds, perhaps thousands, are believed to have died when the government sent in tanks and soldiers to clear Tiananmen Square on the night of June 3-4, 1989, violently crushing six weeks of protests.

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

Meanwhile, China censors blocked internet access to the terms "six four," "23," "candle" and "never forget" on Monday, broadening extensive efforts to silence talk about the anniversary.

Searches for the terms related to the anniversary, such as "six four" for June 4, were blocked on Sina Weibo, the most popular of China's Twitter-like microblogging platforms. Users encountered a message that said the search results could not be displayed "due to relevant laws, regulations and policies."

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"It's that day again and once more numerous posts are being deleted," a Sina microblogger wrote. Sina was not immediately available for comment.

China's censors also blocked access to the term "Shanghai stock market" on microblogs after the index fell a bizarre 64.89 points on the anniversary.

PhotoBlog: Thousands remember Tiananmen Square crackdown

In another twist, the Shanghai Composite Index opened at 2346.98 points on the 23rd anniversary of the killings in either a deft piece of manipulation or an uncanny double coincidence. The numbers 46.98 are June 4, 1989, backwards.

"Whoa, these figures are too freaky! Very cool!" said a microblogger. "The opening figure and the drop are both too creepy," said another. 

For more coverage of China, see Behind The Wall

The anniversary of the date on which troops shot their way into central Beijing in 1989 has never been publicly marked in mainland China.

The government has never released a death toll of the crackdown, but estimates from human rights groups and witnesses range from several hundred to several thousand.

Yao Jianfu, author of a new book of interviews with Chen Xitong, the Beijing mayor at the time of the crackdown, told Reuters that Chen had said "this was a tragedy that should have been averted but wasn't".

"I never foresaw there would be shooting, because Mao Zedong said that ordinary people should not be shot at and suppressing student protests comes to no good," said Yao.

The government has restricted the movements of dozens of dissidents, former prisoners and petitioners during the anniversary period and warned them against speaking to journalists or organizing activities, said Songlian Wang of rights group Chinese Human Rights Defenders.

A coalition of lawyers and rights activists began a one-day fast in their homes on Monday to commemorate the anniversary, said a Shandong-based lawyer, Liu Weiguo.

Tens of thousands of people are expected to attend a candlelight vigil in Hong Kong, said organizers, who had erected a replica of the Goddess of Democracy that was built in Tiananmen Square in 1989.

Chinese tourists stopped on Tiananmen Square shook their heads and appeared mystified when asked about the anniversary. There were no obvious signs of extra security on the already well-guarded square.

But a trinket vendor said he was well aware what day it was.  "Do foreigners also know about June 4?" he asked a Reuters reporter in a hushed tone, looking around to make sure nobody heard him. "I think it is important we remember but nobody will talk about it now." 

Reuters and msnbc.com's Alastair Jamieson contributed to this report.

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