In a Facebook post Tuesday, Tsai said China had shown that it not only had no intention of reflecting on "that year's mistake" but also planned to continue covering up the truth about the incident. Tsai cited comments Sunday by China's defense minister at a forum in Singapore defending the army's bloody assault on protesters and Beijing citizens, as well as Hong Kong's refusal to allow entry to former student leader Feng Congde.
Tsai wrote: "Please rest easy, Taiwan will absolutely adhere to democracy, adhere to freedom, regardless of threats or infiltration."
Chinese overseas are reporting they are being blocked from posting on a popular Chinese social networking site.
Three people said on Twitter that their attempts to post on Weibo were greeted with an error message saying that users with an overseas IP address could not make posts on the China-based service.
China restricts information before and during the 30th anniversary of a deadly military crackdown on pro-democracy protesters in Beijing's Tiananmen Square. There is virtually no mention in mainland China of the crackdown that took place the night of June 3-4, 1989, and is believed to have killed hundreds and possibly thousands of people.
Weibo did not respond immediately to a request for comment.
Pro-democracy activists in Hong Kong are preparing for a candlelight vigil commemorating the Tiananmen protests and remembering the victims of the crackdown.
The semi-autonomous territory is the only region under Beijing's jurisdiction which has a significant public commemoration of the 1989 crackdown. Hong Kong has a degree of freedom not seen on the mainland as a legacy of British rule.
The event beginning at 8 p.m. Tuesday is expected to attract tens of thousands of participants.
At the University of Hong Kong, a dozen students laid bouquets at the "Pillar of Shame," a sculpture by Danish artist Jens Galschiot commemorating the crackdown's victims.
"Just because I wasn't born then and never experienced the event, there's no stopping me from reminding others like me of this and carrying on the collective memory," said student Donald Chung, 18.
China is keeping up its practice of removing dissidents from contact around sensitive political dates on the 30th anniversary of the Tiananmen Square crackdown.
Individuals whose views are considered threatening are typically taken for what are euphemistically called "vacations" far from home. Others are placed under house arrest or their movements and communications are curtailed.
A half-dozen activists could not be reached by phone or text Tuesday, and one who responded, Beijing-based Hu Jia, said he was taken to the eastern coastal city of Qinghuangdao on May 30 by security agents. Though he was able to answer the phone, guards were by his side and he was only able to say a few words. "This is a reflection of their fears, their terror, not ours," Hu said.
Rights groups say special restrictions also were placed on members of the Tiananmen Mothers group, including Zhang Xianling, 81, and Ding Zilin, 82, whose sons were killed in the military assault on the night of June 3-4, 1989, that is believed to have killed hundreds and possibly thousands of people.
The European Union is mourning the victims of the 1989 crackdown on Tiananmen pro-democracy protests on its 30th anniversary and calling on China to release pro-democracy activists.
In a statement, EU foreign policy chief Federica Mogherini recalled how the European Council denounced the "brutal repression" in Beijing at a June 1989 meeting and said the Communist regime needs to account a full account of its actions three decades ago.
Mogherini said: "Acknowledgement of these events, and of those killed, detained or missing in connection with the Tiananmen Square protests, is important for future generations and for the collective memory.
Mogherini added: "We expect the legal safeguards and due process rights of those detained in connection with the 1989 events, or with current activities to commemorate it, to be respected."
China has accused U.S. Secretary of State Mike Pompeo of smearing its domestic and foreign policies in a critical statement he issued on the 30th anniversary of the crackdown on the 1989 Tiananmen Square protests.
A Chinese spokesman said in a post Tuesday on the website of the Chinese embassy in Washington, D.C., that Pompeo's statement "grossly intervenes" in China's internal affairs and is "an affront to the Chinese people and a serious violation of international law."
Pompeo's statement saluted the protesters and urged the Chinese government to make a full public accounting of those killed in the crackdown. It added that America's hopes that China would become a more open and tolerant society have been dashed.
Chinese authorities have stepped up security around Tiananmen Square in central Beijing, a reminder of the government's attempts to quash any memories of a bloody crackdown on pro-democracy protests 30 years ago.
Extra checkpoints and street closures greeted tourists who showed up early Tuesday morning to watch the daily flag-raising ceremony. An honor guard marched across a barricaded street and raised the Chinese flag.
Foreign journalists were not allowed onto the square to record events.
Hundreds, if not thousands of people are believed to have been killed in 1989 when the government sent in the military to clear Tiananmen Square of protesters in an operation that began the night of June 3 and ended the following morning.
Any commemoration of the event is not allowed in China.