Activists gathered in central London Saturday in support of a pro-Palestinian group recently outlawed as a terrorist organization in the UK.

Police arrested some of the hundreds of protesters who gathered outside Parliament in London to defy a ban on the group Palestine Action, which has been deemed a terrorist organization by the government.

Defend Our Juries, the campaign group organizing the protest, said 1,500 people were taking part, holding signs reading “I oppose genocide, I support Palestine Action.”

Within minutes, police began arresting the demonstrators, as bystanders chanted “Shame on you."

“Expressing support for a proscribed organization is a criminal offence under the Terrorism Act,” the Metropolitan Police force said on social media. “Where our officers see offences, we will make arrests.”

More than 700 people were arrested at earlier protests, and 138 have been charged under the Terrorism Act.