There are a number of things that could cause the ship to turn around, like lack of food and water or problems with the engine.

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.

Thunberg and 11 other activists are on board a ship headed to Gaza with aid supplies, but the IDF has said it does not intend to allow the ship to dock.