China's police kept a tight watch on surviving families of the Tiananmen Square massacre in Beijing on Monday, marking the 29th anniversary of the military crackdown on a student-led pro-democracy protest that remains a taboo in China, Hong Kong media reported.

A handful of members of Tiananmen Mothers, a group formed by parents of students killed in the bloody crackdown who have been calling for a redress and accountability for those responsible, gathered at the Wan'an Public Cemetery, 15 kilometers west of Beijing, to mourn the loss of their loved ones.

Plain-clothed police officers were wandering inside the cemetery, keeping watch on the mourners while a heavy police presence was seen outside, blocking off public access, Zhang Xianling, who lost her 19-year-old son in the crackdown, told Hong Kong's Cable TV News.

The families were transported to the cemetery in vehicles arranged by the authorities, broadcaster Radio Television Hong Kong quoted another member, Duan Changqi, as saying.

"We understand the path to seeking justice for you will be long and hard," Duan said. "But still, even down to only one of us, we will not give up, never ever give up."

On the night of June 3, 1989, soldiers opened fire on the pro-democracy protesters who had occupied the square for weeks, acting on Chinese leaders' order to disperse the crowd. The crackdown lasted through the night and left hundreds, if not thousands, dead, though no official count has ever been released.

The Chinese government has always denied any wrongdoing, first describing the event as a "counterrevolutionary riot," then as "political turmoil" that was settled and needs no more attention.

U.S. Secretary of State Mike Pompeo issued a statement Sunday urging China to face its past and respect the universal rights and people's fundamental freedoms.

Pompeo said that on the anniversary of the "violent suppression of peaceful demonstrations," the United States urges the Chinese government "to make a full public accounting of those killed, detained or missing."

China should also "release those who have been jailed for striving to keep the memory of Tiananmen Square alive" and "end the continued harassment of demonstration participants and their families," he said.

Meanwhile, Taiwan's President Tsai Ing-wen on Monday marked the anniversary by suggesting that if Chinese authorities could face up to what happened, admitting the violent nature of the incident, it "could possibly turn the unfortunate history into the foundation of freedom and democracy" as in the case of democratic Taiwan.

Writing on her Facebook page, she drew a parallel with how her government addressed wrongs committed during the decades of authoritarian rule in Taiwan, including establishing a committee to redress unjust cases, seek truth and compensate families of victims.