In a statement challenging claims made by organizers of the protest, the Met said, “We are confident that anyone who came to Parliament Square today to hold a placard expressing support for Palestine Action was either arrested or is in the process of being arrested.”

The claim that only a fraction of those who violated the law were apprehended “simply isn’t true,” police continued.

While around 500 to 600 people attended the rally, many were onlookers, media or people not holding placards in support of the banned group, the statement continued.

Those apprehended were taken to Prisoner Processing Points in Westminster area, while those whose details could be confirmed were released on bail, “with conditions not to attend any further protest in support of Palestine Action,” the statement concluded.

Defend Our Juries, an NGO supportive of anti-Israel initiatives that organized Saturday’s protest, tweeted that “The police are struggling to arrest everyone, as there are too many of us!”

In a subsequent tweet, the group said: “Mass arrests under the Terrorism Act are ongoing at Parliament Square. [Protesters are] being arrested for holding signs in opposition to genocide and the ban of Palestine Action.”

Palestine Action was outlawed on July 2 after its followers vandalized two aircraft at a Royal Air Force base on June 20, according to Reuters.

British Home Secretary Yvette Cooper had sought the proscription under section 3 of the Terrorism Act 2000. The measure, passed by a significant majority in the House of Commons (385 to 26), makes it a crime to belong to or support Palestine Action, placing it on the same legal footing in the U.K. as groups such as Al-Qaeda and Islamic State.

The House of Lords also backed the initiative, and the Court of Appeal in London rejected an appeal to block the ban.