Amid ongoing anti-government protests in Hong Kong, police said that they foiled a second bomb plot in under a week after officers arrested three men allegedly testing home-made devices and chemicals in a secluded area.

The suspects were testing the strength of remote-controlled devices, which were intended for use at mass protests, the police said on Saturday, but it was unclear which chemicals or explosives were involved as the bombs had been detonated, the South China Morning Post reported..

In the early hours of Saturday, acting on intelligence, officers from the organised crime and triad bureau ambushed the trio in Tuen Mun as they carried out tests.

Officers also seized a radio-controlled detonation device and protective gear, including shields, bulletproof vests, a steel plate and gas masks at the scene.

The tools were believed to have been used during the tests.

“The amount (of explosives) was not a lot. But intelligence showed there were two purposes behind the plot – one was to upgrade the power of the bombs, and the other to launch attacks at future assemblies or rallies,” Senior Superintendent Steve Li Kwai-wah said.

Saturday’s operation came as police said three men and two women, aged 15 to 18, had been arrested in suspected connection with the death of a 70-year-old man who was hit by a brick during a fight between masked protesters and Sheung Shui residents last month.

Earlier in the month, Hong Kong’s protests are largely leaderless and organised online. They were initially sparked by a now-abandoned attempt to allow extraditions to the mainland but have since morphed into a popular revolt against Beijing’s rule.

Radicals had caused extensive damage to 85 of 94 MTR stations, so far.

Affected facilities include ticketing machines, surveillance cameras, lifts and escalators and rolling shutters.

In November, China had accused UK human rights chief, Michelle Bachelet of “inappropriate” interference in the country’s affairs, after she called for investigations into alleged excessive use of force by police in Hong Kong.

Hong Kong’s protests started nearly six months ago in June against proposals to allow extradition to mainland China, a move many feared would undermine the city’s judicial independence and endanger dissidents.

In 2018, the Hong Kong government had disqualified the candidacy of another pro-democracy activist, Agnes Chow, for the Legislative Council by-election in March of the same year due to her stance on advocating self-determination for the former British colony.

The controversial China extradition bill was withdrawn in early September but the movement has morphed into a wider campaign for greater democracy and against alleged police brutality.