In the UK, hundreds gathered in London's Parliament Square before marching toward Whitehall, home to government offices. Demonstrators waving Palestinian flags shouted, "Free Palestine" and "Don't bomb Gaza."
As the crowd spilled into the streets, traffic came to a halt, with some bus drivers honking in solidarity. Police later blocked protesters from advancing to Trafalgar Square, leading to confrontations and several arrests. Smaller protests were also reported in other parts of the capital.
In Greece, thousands marched in Athens toward the Israeli Embassy, chanting "End the genocide in Gaza" and "Break the blockade, free Palestine."
Organizers read a joint statement condemning Israel for violating international law and stressing that the flotilla's mission was a legitimate attempt to deliver humanitarian aid.
Parallel protests took place in Thessaloniki, Patras, Chania, Lesbos, Chios, Volos, and Larissa, with participants calling for the immediate release of 27 Greek nationals detained aboard the flotilla.
Israeli naval forces attacked the flotilla as it approached Gaza's coast late Wednesday and detained at least 443 activists on board, organizers said.
The International Committee to Break the Siege on Gaza (ICBSG) confirmed that 22 ships have been attacked and seized by Israeli forces, and 19 are believed to have been attacked, but it has not yet documented them.
Of the four vessels still remaining, two support ships turned back, while the vessel Marinet continued sailing toward Gaza but was still far away after a late arrival due to technical malfunctions, it added.
The flotilla, loaded mainly with humanitarian aid and medical supplies, set sail at the end of August. It was the first time in years that around 50 ships sailed together toward Gaza, carrying hundreds of civilian supporters.
Israel has maintained a blockade on Gaza, home to nearly 2.4 million, for nearly 18 years, and further tightened the siege in March when it closed border crossings and blocked food and medicine deliveries, pushing the enclave into famine.
Since October 2023, Israeli bombardment has killed more than 66,200 Palestinians, most of them women and children. The UN and rights groups have repeatedly warned that the enclave is being rendered uninhabitable, with starvation and disease spreading rapidly.
