Authorities in London have arrested nearly 900 people during a protest in support of the banned group Palestine Action, police say.

The new tally, announced on Sunday, highlights the strict approach that police have taken against the demonstrators, who organisers insisted were nonviolent.

The Metropolitan Police said they arrested 890 people on Saturday, including 857 on suspicion of showing support for a proscribed group. Thirty-three others were detained for allegedly assaulting officers and other public order offences.

Defend Our Juries, the campaign group that organised Saturday’s protest, also rejected police claims that the demonstrators were violent.

“Among the 857 arrestees were vicars and priests, war veterans and descendants of Holocaust survivors, retired teachers and healthcare workers,” the group said in a statement.

It accused the police of making “many false claims and attempts to smear the protesters” to justify arresting peace demonstrators with signs that read: “I oppose genocide – I support Palestine Action.”

“While the Met has failed to provide any evidence backing up their claims, video footage clearly shows the Met violently arresting people, wielding their batons and pushing people to the ground,” Defend Our Juries said.

“We’re nonviolent, how about you?”

The Press Association news agency reported that police drew batons during clashes with protesters. Officers forced their way through the crowd while carrying arrested demonstrators and were seen in shouting confrontations with demonstrators.

Water and plastic bottles were thrown at police, the agency said, while several protesters fell in a crush. One man was photographed with blood streaming down his face after being arrested.

Amnesty International UK, which deployed observers to monitor the protest, also disputed police claims that demonstrators had “co-ordinated” violence at the rally.

“Our observers witnessed the Defend Our Juries protest being entirely peaceful,” the group said.

It called the scenes of the arrests a “shocking demonstration of how the UK’s overly broad terrorism laws are being used to suppress free speech”.

“Police officers, on a number of occasions, were aggressive towards supporters of the protests,” Amnesty said.

“This included violently shoving people away and pulling out batons to make space whilst protesters were arrested and hauled into police vans.”

However, Deputy Assistant Commissioner Claire Smart had earlier claimed that officers faced “co-ordinated” violence during the demonstration.

“You can express your support for a cause without committing an offence under the Terrorism Act or descending into violence and disorder, and many thousands of people do that in London every week,” she said in a statement.

Rallies were also held in Belfast and Edinburgh. Police Scotland said two men, aged 67 and 82, were arrested and charged with “terror” offences while a third man, 63, was charged with a hate crime.

The protests are the latest in a wave of demonstrations against the UK government’s decision to proscribe Palestine Action under the Terrorism Act 2000.

The group, which has targeted arms factories and other sites linked to weapons exports to Israel, was banned after it claimed responsibility for spraying two Voyager refuelling and transport planes at a military base with red paint.

Being a member or expressing support for Palestine Action is now a criminal offence punishable by up to 14 years in prison.

In July, United Nations human rights experts raised concerns about what they called the “unjustified labelling of a political protest movement as terrorist”, arguing that “acts of protest that damage property, but are not intended to kill or injure people, should not be treated as terrorism”.

Meanwhile, the Home Office is appealing a High Court ruling allowing Palestine Action’s cofounder Huda Ammori to pursue a legal challenge against the ban.

Ammori launched proceedings against the decision by former Home Secretary Yvette Cooper to proscribe the group, arguing the move unlawfully criminalised political dissent.

The weekend protests were held as Israel is intensifying its assault on Gaza, which academics, leading rights groups and UN experts have described as a genocide.

According to UK media reports, British forces have been flying surveillance drones over Gaza in support of Israeli operations.