Greta Thunberg and "Game of Thrones" actor Liam Cunningham are among 12 activists aboard the Madleen, which is operated by the Freedom Flotilla Coalition, that is on its way to Gaza.

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

The group is carrying supplies for Gazan Palestinians and protesting what they say is “Israel’s “illegal, decades-long blockade, and ongoing genocide” in the enclave.