A flotilla carrying humanitarian aid and activists, including Swedish climate campaigner Greta Thunberg and Irish poet Sarah Clancy has set sail from Barcelona to try to "break the illegal siege of Gaza", organisers said.
Some 20 vessels set off from the Spanish port city just after 3.30pm to "open a humanitarian corridor and end the ongoing genocide of the Palestinian people", said the Global Sumud Flotilla.
They did not say how many ships would set sail or the exact time of departure.
The flotilla is expected to arrive at the war-ravaged coastal enclave in mid-September.
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"This will be the largest solidarity mission in history, with more people and more boats than all previous attempts combined," Brazilian activist Thiago Avila told journalists in Barcelona last week.
Organisers say that dozens of other vessels are expected to leave Tunisian and other Mediterranean ports on 4 September.
Ms Clancy, who is from Galway, is part of the Irish delegation setting sail today.
People Before Profit-Solidarity TD Paul Murphy has confirmed that he will travel to Tunis in Tunisia to join the flotilla.
Activists will also stage simultaneous demonstrations and other protests in 44 countries "in solidarity with the Palestinian people", Ms Thunberg, part of the flotilla's steering committee, wrote on Instagram.
As well as Ms Thunberg, the flotilla includes activists from several countries, European politicians and public figures such as former Barcelona mayor Ada Colau.
"We understand that this is a legal mission under international law," left-wing Portuguese politician Mariana Mortagua, who will join the mission, told journalists in Lisbon last week.
Previous attempts
The Global Sumud Flotilla describes itself as an independent group not linked to any government or political party. Sumud means "perseverance" in Arabic.
Israel has already blocked two attempts by activists to deliver aid by ship to Gaza, in June and July.
In June, 12 activists on board the sailboat Madleen, from France, Germany, Brazil, Turkey, Sweden, Spain and the Netherlands, were intercepted by Israeli forces 185km west of Gaza.
Its passengers, including Ms Thunberg, were detained and eventually expelled.
In July, 21 activists from ten countries were intercepted as they tried to approach Gaza in another vessel, the Handala.
The humanitarian situation in Gaza has worsened in recent weeks.
The United Nations declared a state of famine in the territory this month, warning that 500,000 people face "catastrophic" conditions.
The war in Gaza was triggered by an unprecedented cross-border attack by Palestinian group Hamas into Israel on 7 October 2023, which resulted in the death of 1,219 people, mostly civilians, according to an AFP tally based on official data.
Israel's retaliatory offensive has killed at least 63,371 Palestinians, most of them civilians, according to figures from the health ministry in Hamas-run Gaza. The UN considers those figures reliable.
