If the public would not join hands to stifle its growth, he could not rule out the possibility of raising the current threat level from “moderate” to “high”, he said.

Police have confiscated at least five guns and foiled more than 10 bomb cases since the anti-government protests began last June.

The seized weapons, including 2kg of the powerful explosive TATP and an AR-15 rifle, have been commonly used in terror attacks overseas. This has prompted local officials to study the possibility of building terrorist cases by using the United Nations (Anti-Terrorism Measures) Ordinance, a piece of local legislation adopted after the attacks of September 11, 2001, when the UN Security Council resolved that countries should beef up laws against extremist violence.

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Both the UN-mandated legislation and the local Crimes Ordinance carry a maximum term of life imprisonment for convicted bomb makers. But Lee said the former empowered the government to freeze suspected terrorists’ property, thereby cutting off their financing and halting their recruitment.

“You cut off the oxygen and disallow the group to grow. These are all preventive measures which other ordinances may not so effectively allow,” he said.

Lee added that resorting to such drastic measures would have “an education and announcement effect”, letting the public know the gravity of the situation.

“Call a spade a spade, in other words. If a heinous act is actually a terrorist act, then using the appropriate law gives that message and [places things in] the right perspective.”

Under the UN ordinance, Hong Kong’s chief executive can apply to the Court of First Instance for an order to designate a suspect as a terrorist or terrorist associate.

Lee brushed off the suggestion that invoking the UN ordinance could serve a political rather than a security purpose, adding that the authorities only took cases to court based on evidence.

While not ruling out the possibility of raising the local threat level, Lee said: “But at the moment, I think we are at a stage where we see a developing trend. But we are also at a stage where we can stop it. I remain confident that our law enforcement agencies are on top of it.”

When dealing with the threat alerts, the minister said, the government must look at how organised, well financed and sophisticated the enemies were, as well as its ability to eliminate their threat.

Should the threat level be raised to high, he said, the city would need to step up security, including sealing off high-risk locations, maintaining high-profile patrols, and conducting bag searches and security checks on people in public.

The minister blamed last year’s protest violence for inuring people to the problem, and urged everyone to condemn radical action.

“It’s important that we collectively cut it. So anybody who stands in the [way of a] police operation when they take action against these potential terrorists, it is a serious matter. They have to be dealt with as well because these are the people who are providing oxygen to the terrorists.”

He also identified the internet as being part of the problem, providing platforms for people to plan and spread radical ideas.

“They socialise, discuss among themselves, reinforce and echo each other, so that this extreme idea gets amplified and aggravated. The self-reinforcement gets to such a stage that then they become radicalised,” he said.

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Lee also raised suspicions about unnamed forces organising and training the radicals.

“I think if you look at the organisation of the activities, the resources that they get and the division of labour – that is so clear among some of the activities – and the strategy and plan … this isn’t something that could be done by the men in the street, right? So obviously, they have been [receiving] training,” he said.

Police seized more than two tonnes of explosives and chemicals in early March, arresting at least 17 people. Detectives suspected they were linked to three bomb plots in January and February, when an explosive device went off at a public hospital, as did another on a train at Lo Wu station, while a third was found at the Shenzhen Bay border control point.

Some people claimed responsibility on a social media platform before and after the plots, saying they intended to pressure the government into closing the city’s border with mainland China in response to the spread of the coronavirus.

In 2018, the Security Bureau set up the Interdepartmental Counter Terrorism Unit (ICTU), composed of officers from six disciplined services – police, immigration, customs, correctional services, the fire service and the Government Flying Service. As political unrest had intensified, Lee said, the unit was focused more on reviewing strategy and advising him on the right counterterror measures. The team also needed to prevent local extremists from connecting with others overseas, he said.

Without going into details, Lee added that staff across the departments collected and shared intelligence, enabling the city to neutralise groups before they could act.

“There are a lot of behind-the-scenes heroes who sacrifice their days and nights, who may lose their sleep while other people are enjoying their lives,” he said.

“When eventually they have neutralised vicious gangs and terrorist radicals, they are the people who then go to sleep and get back to their normal day to work. There are so many unsung heroes and I thank them all.”