(Bloomberg) -- Hong Kong police said a radio-controlled improvised explosive device was detonated near a police car on Sunday evening, the first time one has been used during months of unrest.

The device was set off in Mong Kok in Kowloon about 10 meters (33 feet) away from a police car that had come to the scene to clear barricades, Suryanto Chin-chiu, superintendent of the explosive ordinance disposal bureau, told reporters on Monday. No injuries were sustained because no one was close enough to the device when it was detonated, he said.

The aim of the bomb was to “kill and seriously harm police officers at the scene,” Suryanto said. The bomb appeared homemade but it “required a certain level of chemical knowledge,” he said, adding that police had no suspects yet.

The use of explosives marks a significant escalation in pro-democracy protests that started out peacefully in June, with hundreds of thousands of residents marching in the streets in opposition to a bill that would have allowed extraditions to mainland China. While the bill has since been withdrawn, the protests have become increasingly violent -- particularly since Hong Kong Chief Executive Carrie Lam invoked a colonial-era emergency law earlier this month to ban protesters from wearing face masks.

In recent weeks, protesters have set fires near police stations, hurled makeshift petrol bombs at riot police, and bashed in glass kiosks at train stations and storefronts tied to mainland Chinese businesses. A Hong Kong police officer was slashed in the neck by a protester in a subway station on Sunday and remains in the intensive care unit, police said on Monday.

To disperse large crowds of demonstrators, the Hong Kong police force has used tear gas, pepper spray, water cannons and rubber bullets. Two teenagers were also shot this month during protester clashes with police.

The city’s rail operator has begun to shut their operations early, while restaurants, grocery stores, and malls have also closed their doors early too.

‘Feeling Desperate’

Thousands of protesters gathered on Monday evening in the city’s central district in a police-sanctioned rally in support of the Hong Kong Human Rights and Democracy Act, proposed U.S. legislation aimed at reviewing the city’s special trading status and potentially sanctioning some Chinese officials. One of the bill’s sponsors, U.S. Senator Josh Hawley, a Missouri Republican, was in Hong Kong the past few days and met with pro-democracy activist Joshua Wong.

The crowd of black-shirted protests wore face masks in defiance of the city’s mask ban and waved American flags, with some holding signs appealing to U.S. Congress and the American people for their support.

The Hong Kong government is “trying to keep people from coming out, but we won’t surrender,” said Mok, a 23-year-old fine arts student who declined to give his first name. “We want to let the world know that we will keep coming out and protesting until the Hong Kong government takes some action on our demands.”

He said he was a peaceful protester but that he supported the violent actions of other demonstrators, including the home-made explosive detonated over the weekend.

“People are feeling desperate about the situation,” he said. “What led to that explosive wasn’t terrorists targeting innocent people but desperate people just responding to the police violence.”

(Updates with Monday protest from eighth paragraph.)

To contact the reporters on this story: Shelly Banjo in Hong Kong at sbanjo@bloomberg.net;Shawna Kwan in Hong Kong at wkwan35@bloomberg.net

To contact the editors responsible for this story: Daniel Ten Kate at dtenkate@bloomberg.net, Brendan Scott, Ben Sharples

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