Greta Thunberg, the 22-year-old Swedish climate activist, has embarked on a high-stakes humanitarian mission to Gaza, sailing aboard the Madleen, a vessel carrying urgent supplies for civilians trapped under Israel’s prolonged blockade.

Israel warned Wednesday that it is “prepared” to “act accordingly” to stop Greta Thunberg’s so-called Freedom Flotilla Coalition from reaching Gaza — as the eco-activist frolicked and filmed smiling social media content on the Mediterranean Sea.