Climate campaigner Greta Thunberg and 11 other activists set sail on June 1 for Gaza on a ship aimed at “breaking Israel’s siege” of the devastated territory, organizers said. Israel’s defense minister has vowed to prevent an aid boat carrying Greta Thunberg and other activists from reaching the Gaza Strip.

The boat Madleen, operated by Freedom Flotilla Coalition, embarked from the Sicilian port of Catania in southern Italy for the shores of Gaza Strip on June 1.

The almost 20 months of war has torn Gaza apart, often displacing residents multiple times and killing more than 54,000 people, according to the Hamas-run Health Ministry. A U.S.-brokered ceasefire agreed in January collapsed in March as Israel enforced a blockade on all humanitarian aid into the strip.