Israel's Katz said he instructed the military to "take whatever measures necessary" to stop the ship carrying Thunberg and other activists.

Thunberg, a climate campaigner, is among 12 activists aboard the Madleen, which is operated by the Freedom Flotilla Coalition.

Five days after climate activist Greta Thunberg set sail Sunday afternoon along with 11 other activists on a ship carrying aid to Gaza, the group could soon near Israeli waters. Israeli officials have vowed not to allow the ship,