Greta Thunberg and 11 activists, including the Franco-Palestinian MEP Rima Hassan, embarked on Sunday in Catania on board the sailboat Madleenon the way to Gaza to try to break the Israeli blockade.
The expedition, organized by the Freedom Flotilla Coalition, aims to deliver aid and to alert on the humanitarian crisis.
A previous attempt in May had failed. The conscious ship had been damaged. Activists said they suspected an attack on Israeli drones.