Two people have been arrested after Palestine Action claimed to have blockaded the entrance of an Israeli defence company's UK headquarters.
The move comes ahead of proposed government legislation that will ban the group under anti-terror law.
A Palestine Action spokesperson said on Tuesday that activists had blocked the entrance to Elbit Systems in Bristol, and covered it in red paint "to symbolise Palestinian bloodshed".
Avon and Somerset Police later said a 30-year-old woman and a 36-year-old man, both from London, were arrested on suspicion of criminal damage, unauthorised entry to a prohibited place and locking on to a person, object or land to cause serious disruption.
The force said officers were called to the site at around 6.30am.
A police spokeswoman said: "Two people have been arrested following a small protest outside a premises at the Aztec West Business Park, in Almondsbury.
"They remain in police custody and inquiries are ongoing.
"We're committed to facilitating people's right to peaceful protest, but will not tolerate any criminal behaviour."
The arrests come as a draft order was laid before parliament on Monday to amend the Terrorism Act 2000 to include Palestine Action as a proscribed organisation.
If approved, it would become a criminal offence punishable by up to 14 years in prison to be a member of the direct action group or to support it.
MPs and peers are set to debate the legislation on Wednesday and Thursday and, if approved, the ban could come into force by Friday.
A Palestine Action spokesperson said: "While the government is rushing through Parliament absurd legislation to proscribe Palestine Action, the real terrorism is being committed in Gaza.
"Palestine Action affirms that direct action is necessary in the face of Israel's ongoing crimes against humanity of genocide, apartheid, and occupation, and to end British facilitation of those crimes."
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The spokesperson also said the group had occupied the rooftop of UK subcontractor Guardtech Group.
Officers are also at the scene at the site in Brandon, Suffolk.
A Suffolk Police spokesman said: "Officers and specialist negotiators are currently at the location and our immediate priority is to bring this to a conclusion and to ensure the safety of everyone at the scene."
Palestine Action is seeking a legal challenge against the government's bid to proscribe it, with a hearing expected on Friday to decide whether the ban can be temporarily blocked, pending further proceedings to decide whether a legal challenge can be brought.
Commenting on the proscription on Monday, Home Secretary Yvette Cooper said: "The right to protest and the right to free speech are the cornerstone of our democracy and there are countless campaign groups that freely exercise those rights.
"Violence and serious criminal damage has no place in legitimate protests."
(c) Sky News 2025: Two people arrested after Palestine Action claimed it blocked Israeli defence firm's UK site