London's Metropolitan Police confirmed five people -- three men and two women, ranging in age from 26 to 61 -- had been arrested "on suspicion of encouraging support for a proscribed organisation" in London, Cumbria and Yorkshire.

Defend Our Juries has organised several demonstrations against the July 5 Palestine Action ban, leading to hundreds of arrests with police charging scores of people under anti-terror laws.

The campaigners had been due to hold an online press conference Tuesday ahead of another "Lift the Ban" protest in London this weekend, but postponed the briefing after what they called the "dystopian crackdown".

"Counter-terrorism police arrested five of Defend Our Juries' key spokespeople in dawn raids in London this morning over Lift the Ban protests," it said in a statement.

"This is scandalous," a spokesperson added, calling it "an unprecedented assault on free speech in our country".

"This level of political repression is not what we expect in a democracy -- it's the kind of tactic typically associated with authoritarian regimes around the world," the spokesperson said.

A Met spokesperson said the arrests were "part of a proactive investigation" led by its counter-terrorism command into "suspected activity linked to" Palestine Action.

"Those showing support for this particular group, or encouraging others to do so can expect to be arrested, investigated and prosecuted," Chief Superintendent Helen Flanagan added in a statement.

- 'Intimidatory' -

Defend Our Juries vowed to press ahead with its demonstration on Saturday in Parliament Square, claiming 1,000 people had pledged to hold signs saying "I oppose genocide. I support Palestine Action".

More than 700 people who have held up such signs at previous protests over the last two months have been arrested under anti-terror laws for showing support for a proscribed organisation.

Police said Monday a further 47 people had been accused of showing support for a banned group, meaning 114 Palestine Action supporters have now been charged with the offence.

The arrests were made under the 2000 Terrorism Act, which the government also used to proscribe Palestine Action.

Interior minister Yvette Cooper accuses it of orchestrating "aggressive and intimidatory attacks against businesses, institutions and the public".

It was outlawed after the group took responsibility for breaking into a Royal Air Force base in June and spraying two aircraft with red paint, causing an estimated pound7 million ($10 million) in damage.

Palestine Action said its activists were protesting UK arm sales to Israel amid the war in Gaza.

Critics, including the United Nations and groups such as Amnesty International and Greenpeace, have condemned the group's proscription as legal overreach and a threat to free speech.