China increased the presence of security forces on the streets of Beijing and information restriction on Tuesday, the 30th anniversary of the crackdown on the Tiananmen Square democracy protests, to contain any potential commemorative demonstrations.

A large number of uniformed and plainclothes police officers kept close watch in and around the square, as groups of tourists including foreigners visited the political center of the capital. Some journalists were refused entry.

To maintain its firm one-party rule, the Chinese Communist Party justified the 1989 killing of hundreds of protesters and bystanders by declaring it necessary to quell political unrest. Open discussion about the incident remains taboo in China.

(Tiananmen Square on June 4, 2019)

With the 30th anniversary has also come tight control over the availability and dissemination of related information, as authorities appear concerned about foreign media lambasting the one-party system.

In a bid to prevent its people accessing what it considers unsuitable information critical of the ruling Communist Party and government, China has blocked access to many overseas websites such as Google Search, YouTube and Facebook.

Virtual private network software enables internet users in China to circumvent its so-called Great Firewall -- which severely limits open access to the internet -- and visit blocked websites.

With the arrival of the anniversary, however, VPN connections have become unreliable, Beijing-based foreign correspondents have reported.

Following the 1989 death of Hu Yaobang, sacked as general secretary of the Communist Party two years earlier for his liberal leanings, students rallied to call for democracy and government action on rampant corruption. Support for the protest grew as people poured into Tiananmen Square.

(Tiananmen Square on May 4, 1989.)

The protest defied martial law, declared in late May, and inspired big rallies across China. But from late June 3 into June 4, troops and armored vehicles cleared the square by force, killing protesters and bystanders.

In a statement released Monday, U.S. Secretary of State Mike Pompeo said, "We urge the Chinese government to make a full, public accounting of those killed or missing to give comfort to the many victims of this dark chapter of history."

The Chinese Embassy in Washington on Tuesday criticized Pompeo's statement, saying it "grossly intervenes in China's internal affairs, attacks its system, and smears its domestic and foreign policies."

"The Chinese side expresses its strong dissatisfaction and firm opposition to it," the embassy said.

Foreign Ministry spokesman Geng Shuang said at a press conference Tuesday, "China's tremendous development achievements (after the Tiananmen incident) show that the actions taken by the Chinese government at that time were completely correct."

"Political stability, economic development and social progress of the country have maintained and continued," Geng said, adding, "Chinese people will unswervingly move forward along the path of socialism with Chinese characteristics."

While a majority of the Chinese newspapers did not make any reference to the 30th anniversary, the English-language version of the Global Times, an influential tabloid affiliated with the Communist Party, made a rare mention of the incident on Monday.

"Today's China obviously has no political conditions to suddenly reproduce the riot of 30 years ago," the newspaper's opinion piece reads. "Chinese society today has seen enough of the political tragedies that occurred in other nations such as the Soviet Union."

(People head to Tiananmen Square on June 4, 2019)

Related coverage:

China photographer unveils rare Tiananmen pictures on 30th anniv.

China's Tiananmen Square crackdown remembered 30 years on

U.S. urges China to make full account of Tiananmen Square protesters