EU criticism of China's rule over Hong Kong is unfounded, China's Foreign Ministry said on Tuesday, after an EU report called the disappearance of five booksellers the most serious challenge to the "one country, two systems" principle since the city's return to Chinese control.

The disappearances of the five publishers who sold books critical of Chinese leaders had provoked concern that China was using shadowy tactics to erode the formula under which Hong Kong has been governed since its return to China from British rule in 1997.

One of the booksellers, Lee Bo, a British passport holder, disappeared in December and surfaced in China almost three months later. He has since returned to Hong Kong and said he had not been kidnapped by Chinese authorities as many suspected.

Britain, however, said he was removed under duress, and an annual EU report released Monday said the apparent abductions have called China’s one country, two systems principle into "serious doubt."

"The case raises serious concerns about respect for human rights and fundamental freedoms and about the application of PRC (China) criminal law to acts that are not punishable under Hong Kong law," the report said.

The report goes on to say the case could have an impact on Hong Kong's standing as a global business center.

Gui Minhai, another temporarily disappeared bookseller, held a Swiss passport. Both he and Lee Bo made a statement via Chinese media that they didn't want other countries to get involved in their missing persons cases.

Some people in Hong Kong, however, suspect that is not their wish, and say the former abductees are fearful of retribution should they speak against Beijing.

“In the eyes of the West, [Western] media and in the eyes of Hong Kong people, their statement could not be trusted, because they were under threat,” Joseph Yu-shek Cheng, professor of Political Science of Hong Kong City University, told VOA’s Mandarin Service. “Like when people were executed by ISIS, they were forced to issue statement against their own country.”

Foreign Ministry spokeswoman Hua Chunying said on Monday that EU should "stop interfering in Hong Kong affairs."

"The EU report disregards the facts and makes unfounded criticism about Hong Kong affairs," Hua told reporters at a regular press briefing. "We express our firm opposition to this."

"The Chinese government's determination to implement 'one country, two systems' is unwavering and will not change," Hua added.

The EU report indicates other aspects of "one country, two systems"—including Hong Kong's independent judiciary—works well. But critics of Beijing say findings of the report show disturbing trends regarding Hong Kong’s press and academic freedoms, and that the unresolved disappearance of the five booksellers can only underscore the theme of increasingly restrictive mainland rule.

“The Freedom of the press situation is very serious," Cheng told VOA. "Most Hong Kong media are in the hands of big corporations, and these big corporations, without exception, all have important business in China. That is the reason why media exercise self-restraint.”

Cheng also said Hong Kong’s press freedom ranking declined in recent years, according to reports issued by international group Reporters without Borders. As for Hong Kong’s academic freedom, Cheng said Hong Kong Chief Executive Leung Chun-ying's government has used its power to appoint academic officials in a manner that allows it to exert greater influence over the management of city universities.

“For example, the pro-Beijing Council of the University of Hong Kong last year refused to appoint Johannes Chan to be the vice president of the University," he added. "Hong Kong government appointed Arthur Li to be the Chairman of the board of Hong Kong University, [and] both events arouse great social concern and protest.”

Johannes Chan is said to support student protests.

“Hong Kong's political instability is due to the fact that, for the Communist Party leadership, the democratic aspirations of Hong Kong’s people is unacceptable," said Cheng. "They want to make Hong Kong people understand their definition of the so-called 'one country two systems.' The Party leadership therefore has taken a tough policy on all issues; they want to teach Hong Kong people a lesson.”