Police arrested 139 people outside the US embassy in London during protests against the ban on Palestine Action, with officers saying arrests were continuing. The demonstrations were the largest against the proscription under Andy Burnham’s premiership.

Hundreds gathered in Battersea, south London, carrying signs declaring: “I oppose genocide, I support Palestine Action.” A vigil also took place outside the US consulate in Edinburgh. Organiser Defend Our Juries estimated the London turnout at around 400.

The Metropolitan Police had warned that participants faced arrest and that organisers, people directing others and those providing logistical support would probably be committing an offence. Commander Adam Slonecki said those attending knew supporting a proscribed organisation was unlawful and were deliberately gathering to commit a crime.

Defend Our Juries accused police of seeking to spare the US embarrassment and appease American interests. It argued that Israel’s alleged war crimes depended on US approval. The group said more than 4,000 arrests for supporting Palestine Action had occurred since the ban, accounting for the vast majority of terrorism arrests since last July.

The dispute centres on the criminalisation of support for the organisation. Retired demonstrator Sue Morhall, 79, said American complicity in wars and events in Gaza had brought her to the embassy. Previously arrested “five or six” times, she remained hopeful Burnham might reverse the ban, while speculating that he could wait until the US midterm elections.

The Rev Bill White, 72, said Britain was facilitating what he described as genocide by supplying weapons used against Palestinians. He resigned from Labour after the proscription and said his faith required him to oppose a law he considered wrong.

An appeal against the terrorist designation is due before the UK Supreme Court on 4 November. Home Secretary Shabana Mahmood has maintained her support for the ban despite pressure on the new government to rescind it.

Last month, more than 160 people were arrested or reported for summons at a similar protest outside Labour’s Liverpool conference. There, two activists challenged Foreign Secretary Ed Miliband during a Pizza Express meal, urging him to declare genocide in Gaza and lift the ban. He offered to discuss it another time before they were ushered out.

Police treatment of expressions of support remains contentious. Author Sarah Helm, wife of national security adviser Jonathan Powell, was accused of supporting Palestine Action after a post responding to news that Sally Rooney could no longer sell her books in Britain because of her support for the group. Police judged Helm’s post below the criminal threshold. Yet a London protester was arrested carrying wording that replaced Helm’s “authors” with “retirees”.