(CNN) — Several anti-monarchy protesters were detained in central London ahead of the coronation of King Charles III on Saturday, their group said, as the Metropolitan Police faced scrutiny over their attitude towards protesters at the historic event.

Thousands of people they met This Saturday in central London to celebrate this once-in-a-generation event. But it also attracted protesters, who wore yellow T-shirts and jeered and chanted “Not my king” all morning.

The Republic, Britain’s largest anti-monarchy group, told CNN that police – without giving any reason – detained the anti-monarchy protest organizers.

Around 7 a.m. (2 a.m. ET) police detained six Republican organizers and told them they would be stopped and searched, Republican director Harry Stratton told CNN at the protest.

Graham Smith, Republican CEO, was among those arrested, according to a video shared by the Alliance of European Republican Movements.

Stratton stated that when organizers asked police why they were being detained, they were told they “will find out” after frisking anti-monarchy protesters. After searching them, the police informed the six organizers that hundreds of their “Not My King” banners had been detained and confiscated.

“They didn’t say why they were being held. They didn’t tell them or us where they were being taken. That’s the state’s police business,” Stratton said.

“I think people are quite worried about the reaction of the police. But the reaction of people towards us has been very friendly,” he added.

Group published in Twitter This Saturday comments: “The right to peaceful protest is over.”

Members of the environmental activist group Just Stop Oil also appear to have been detained in The Mall, opposite Buckingham Palace, Britain’s PA Media news agency reported, adding that a large group of protesters were seen in handcuffs.

A member of Just Stop Oil was arrested and transferred by the Police. (Photo: Yara Nardi/WPA Pool/Getty Images)

The Metropolitan Police confirmed that several arrests had been made in central London.

“Today we have arrested four individuals in the St Martin’s Lane area. They have been arrested on suspicion of conspiracy to cause a public disturbance,” the agency tweeted.

“We have made several arrests in the Carlton House Terrace area. Several people have been detained on suspicion of disorderly conduct,” police continued on Twitter. “Three other people were arrested in the Wellington Arch area. They are being held on suspicion of possessing items that cause criminal damage.”

Human Rights Watch, a non-profit campaign group, said the coronation arrests were “something you would expect to happen in Moscow, not London,” according to a statement obtained by PA Media.

Anti-monarchy groups expressed concern about the treatment of the protesters. (Photo: Chris Ratcliff/Bloomberg/Getty Images)

Republic said it expected 1,500 to 2,000 people to join the group in their protest in Trafalgar Square, just south of the royal procession route.

“Instead of a coronation, we want an election. Instead of Carlos, we want an election. It’s that simple,” the group tweeted Saturday.

Increased police power

The Metropolitan Police, Britain’s largest police force, have been closely watched hard focus against the protests surrounding the coronation.

“Our tolerance for any disturbance, whether protest or otherwise, will be low,” the agency wrote on Twitter this week. “We will take firm action against anyone who tries to spoil this celebration.”

Ahead of the event, the Metropolitan Police said more than 11,500 police officers would be deployed to London on Saturday, making the coronation the largest single-day deployment in decades.

The operation – called Orbe Dorado – consisted of lining up agents along the procession route, managing crowds and roadblocks, protecting the most prominent people and carrying out searches with special teams.

Facial recognition technology is also planned for use in central London, drawing criticism from human rights groups.

Protesters gathered in central London this Saturday. (Photo: Susannah Ireland/AFP/Getty Images)

“We all have the right to live our lives without scrutiny and surveillance, but all coronation attendees risk having their faces scanned with oppressive facial recognition technology,” said Emmanuelle Andrews of rights group on Twitter Human Liberty.

The operation comes amid growing concern about increasing Police powers to suppress dissent in the UK, following its recent introduction controversial legal text.

Last year, the Police, Crime, Sentencing and Trial Act 2022 “significantly expanded the range of circumstances in which Police can impose conditions on protests.” Under the new law, it is an offense for protesters to “deliberately or recklessly cause a public disturbance,” including causing “serious disturbance.”

In a statement to CNN, Liberty said that these laws “have made it more difficult for people to stand up for what they believe in without running the risk of being criminalized.”

On Tuesday, a new law called the Public Order Act received the royal nod from King Charles, which is the last formality and hurdle before a bill becomes law.

“This will provide the police with the necessary powers to prevent disruption to major sporting and cultural events taking place this summer in England and Wales,” the UK Home Office said in a statement.

The special measures of the law were introduced from Wednesday.

Under this law, entrenched protest tactics such as confinement – ​​in which protesters physically comply with elements such as buildings – can be punished with up to six months in prison or an “unlimited fine”, explained the Interior Ministry.

CNN’s Niamh Kennedy contributed to this article.