Famed Swedish activist Greta Thunberg was released from custody after her arrest early Tuesday at a London protest in support of pro-Palestinian hunger strikers.

Thunberg was released on bail after being arrested for a sign which said "I support Palestine Action prisoners. I oppose genocide," the Prisoners For Palestine group said on US social media company X.

The group noted that two protesters who shut down Aspen Insurance in solidarity with the hunger strikers remain detained at Bishopsgate station.

Thunberg, 22, had been arrested by police officers outside the offices of Aspen, which the group says provides services to Israeli weapons firm Elbit Systems.

She was arrested under the Terrorism Act for holding a sign that read: "I support Palestine Action prisoners. I oppose genocide."

"She has been arrested for displaying an item (in this case a placard) in support of a proscribed organisation (in this case Palestine Action) contrary to Section 13 of the Terrorism Act 2000," City of London Police wrote on US social media company X.

Some activists also sprayed red paint over the front of the building before being detained.

The protest came amid rising criticism of the government over the state of six detainees linked to the banned group Palestine Action, who have been on a hunger strike since November.

Palestine Action was banned in July under the Terrorism Act after members of the group spray painted two Royal Air Force aircraft, causing £7 million ($9.44 million) in damage, according to police. Hundreds of pro-Palestine activists have since been arrested across the UK.

'Totally ridiculous' arrest

Thunberg's arrest drew an international backlash, including by Francesca Albanese, UN special rapporteur on the occupied Palestinian territories, who criticized the UK government and accused it of being part of the coverup of Israel’s genocide.

"To the UK government: the more people you arrest to shamefully cover up Israel's genocide the more decent people will stand up against you in the name of human rights," she wrote on X, with a video of Thunberg's arrest.

Albanese added: "In the end, we will all make sure that the leaders who are complicit with Israel genocide will face justice."

Green Party leader Zack Polanski also spoke out against the arrest, saying Thunberg was arrested "for holding a sign opposing genocide."

"When peaceful protest is a crime, democracy is in deep trouble,” said Polanski, remarking how this is “Happening under a Labour Government.”

Richard Burgon, a Labour lawmaker, called the arrest "totally ridiculous," adding that this is yet another example of why he voted against the Palestine Action ban in Parliament.

Zarah Sultana of the new Your Party said that Thunberg was arrested "for opposing genocide" while Prime Minister Keir Starmer – who she called "complicit in the genocide of the Palestinian people" – walks free.

"He should be arrested and sent to The Hague," said Sultana. (AA)

Update news