HONG KONG (AP) — The top American diplomat in Hong Kong said Monday that it is a “tragedy” to use the semi-autonomous Chinese territory’s new national security law to chip away at freedoms in the Asian financial hub.

“Using the national security law to erode fundamental freedoms and to create an atmosphere of coercion and self-censorship is a tragedy for Hong Kong,” Hanscom Smith, U.S. consul general to Hong Kong and Macau, told reporters. “Hong Kong has been successful precisely because of its openness and we’ll do everything we can to maintain that."

The law, imposed last week following anti-government protests in Hong Kong last year, makes secessionist, subversive, or terrorist activities illegal, as well as foreign intervention in the city’s internal affairs. Any activities such as shouting slogans or holding up banners and flags calling for the city’s independence are a violation of the law regardless of whether violence is used. The maximum penalty is life imprisonment.

Critics see it as Beijing’s boldest step yet to erase the legal firewall between the former British colony and the mainland’s authoritarian Communist Party system.

Since the law went into effect, the government has specified that the popular protest slogan “Liberate Hong Kong, revolution of our time” has separatist connotations and is thus criminalized.

In Hong Kong’s public libraries, books by pro-democracy figures have been pulled from the shelves, including those written by prominent pro-democracy activist Joshua Wong and politician Tanya Chan. The authority that runs the libraries said it is reviewing the books in light of the new legislation.

Many pro-democracy shops that publicly stood in solidarity with protesters have removed pro-democracy notes and artwork that adorned the walls of their stores, fearful that they might violate the new law.

A 23-year-old man, Tong Ying-kit, was the first person in Hong Kong to be charged under the new law, for allegedly driving a motorcycle into a group of policemen while bearing a flag with the “Liberate Hong Kong, revolution of our time” slogan.

Tong appeared in court Monday facing charges of incitement to secession and terrorist activities. He was denied bail.

Separately, pro-democracy activists Agnes Chow, Joshua Wong and Ivan Lam also appeared in court Monday over charges related to a protest last June. Chow pleaded guilty to inciting others to participate in an unlawful assembly, as well as to participating in an unauthorized assembly.

Wong, who was indicted on similar charges, pleaded not guilty. Lam, who was charged with inciting others to participate in an unlawful assembly, also pleaded not guilty. All three were released on bail.

“With the risk of our personal safety, with the threat of life sentencing, we might be worried, and also being targeted by Beijing, but we also encourage the global community to let our voice be heard in the world,” Wong told reporters Monday. "We still hope to let the world know that now is the time to stand with Hong Kong, and now is the time for Hong Kongers to keep our momentum.”

The cases will move to trial and sentencing following a pretrial review for Wong and Lam scheduled for Aug. 5.

A group of about 10 protesters gathered at a shopping mall in Hong Kong’s Central business district on Monday holding up signs calling for city leader Carrie Lam to step down, as well as reiterating protesters’ demands from the pro-democracy movement last year. The demands include an independent inquiry into the police and greater democracy.

Others held up blank pieces of paper as a sign of protest against the suppression of political protest in the city. About 20 riot police later entered the mall, detaining protesters holding up signs, although they did not appear to make any arrests.

“We feel worried that we may be convicted for expressing our views,” said protester Anthea Wong. “That’s why we are using white paper instead.”

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Associated Press journalist Katie Tam contributed to this report.